Well, if I had my way...
RE4- Umbrella would still be around, but it is clear that it is on its last legs, but dear old Oswell makes one last grab to try finding the elixir of immortality. He has discovered Las Plaga in Spain possibly years ago and studies it, infecting the villagers and turning them to loyal servants. He takes control of the Alpha Plaga, and does regain a bit of his strength, but discovers that he needs to consume the flesh of certain people to make him more powerful and Ashley is one of the chosen ones who has the right genes to make him stronger. He has been having these chosen ones kidnapped all over the world, and of course, since the president's daughter is kidnapped, Leon is a bad enough dude to save her. Meanwhile; Chris, Jill, and possibly Barry or Claire are on the hunt for Spencer and so is Wesker. They have a lead that he is somewhere in...Spain? England? Idk...and the trio teams up with Leon while Wesker is in the shadows. Sergei could be the penultimate boss I guess...and Spencer...hmmm well, I would say that he has munched on enough people to become a powerful last boss. When he is defeated, it is he the end of him and Umbrella. I would say that there would be three campaigns, and they would be single player. Leon would be on his mission to save Ashley, Chris, Jill and Barry/Claire would have dedicated sections, and Wesker would be like Ada in Separate Ways and work from behind the scenes. I know this may seem a lot, but its what I thought of.
RE5- Chris would still be the main character and is actually doing this by himself! Chris has two missions: Jill/Claire/Rebecca/or whoever went to investigate the rumor of a new virus, but he has been a long time since anyone has heard from them, and Chris has to go and find them. His other mission is to take over the investigation once he is thrown into a Biohazard situation. I'm not sure if it should be the return of Las Plagas or something else, but either way Wesker is behind it. Tricell would still be the villains as he has convinced Excella to use the power and resources to help him with his plans. There are parts where the player would fight Wesker, largely unchanged from canon except Sheva isn't there to help you. Also no mind controlled Jill or anything like that. They would probably get rescued either early or late in the game and act as support. The finale will not happen in a volcano, even by RE standards, what happened there was just so goofy to behold. I...honestly have no clue where the final battle would take place, but it will mark the end of Wesker. Happy Ending!
Umbrella Chronicles-Okay so, this will still be a rail shooter, retelling certain events, only it obviously won't tell the downfall of Umbrella. Sergei is still the main villain, and Chris and Jill found his hideout in Russia creating ...idk Talos? Instead of getting killed, he manage to escape for RE4. Wesker's bossfight would be Ivan infected with Las Plaga, which he didn't know about yet. Along the way, Sergei would've sacrificed the Red Queen so Wesker wouldn't have it, but Wesker found something that he missed...the whereabouts of Spencer.
Darkside Chronicles: Yes, believe it or not. I do have a idea for this. Its still a rail shooter and it remains largely the same, but major changes in Operation Javier. Jack Krauser does not exits at all, and would be replaced by Ark Thomson who happens to be there as he is hired as a private investigator to look for someone's missing daughter. They both met up on Javier's private island that he uses for a personal fortress and smuggling ring since he is a powerful man. He is still kidnapping girls for his ill daughter Manuela, and she ran away still. Ada is on the island as well, and when she meets with Leon, he is genuinely shocked and surprised that she is alive instead of being indifferent to her return when he thought she was dead all this time!! This would lead into the RE2 segment which once again, remains unchanged. Leon and Ark meets with Manuela and use her as a guide to infiltrate the compound. T-Veronica is still in use though and Manny is carrying a new mutation of the virus. That is why Ada is here, for her blood as sample. This will also lead into the Code Veronica portion, same as above. Ada isn't the only one looking for the Veronica Virus, Hunk has been sent in to retrieve it as well for Umbrella as a final chance to get it, and could battle Ada for it, but he lost...or did he? Anyway in Ark's quest, it could either be that he found some of the girls and manage to escape with them, or find that they are dead. The Javier fight...instead of being a humongous plant spider and on an invisible time limit, he becomes a stronger version of his infected wife and Ada could lend a hand by doing what she does best...tossing Leon and Ark a Rocket Launcher lol. The day is save, Manuela(and the surviving girls) leave he island, Ada has the sample to wants and bring it to Wesker. Hunk could have arrive on the island in the aftermath if not in the main game and takes a mutated sample from Javier or the wife.
Revelations 1- Right, here are the changes. Barry would be Jill's Partner while Parker is with Raymond. Terragrigia is not a Aqua city, but it still is a coastal city that was hit by terrorism before it was destroyed, Keith and Quint are not playable, none of this Dante inferno quoting. The BSAA and the FBC are in a joint operation against Jack Norman's organization I guess called Eclipse or Surge instead of their original name. Barry and Jill are paired up with FBC agents Parker and Raymond to investigate the Queen Zenobia when they believe that Jack and his men has taken over the ship. Chris and Jessica meanwhile are exploring the ruins of Terragrigia when they notice suspicious activities. In this version, Jack uses the T-Abyss as a tool of revenge against the world for killing his longtime friend Oswell Spencer, as maybe he would be the man's sword of vengeance. He secretly teamed up with Morgan Lansdale who supplied him with the virus, and after the Terragrigia panic, left Jack and his men to die. He lives, and hid in the ruins of the city with the last of his men and plan for resurgence. Raymond and Jessica would be plants by Lansdale to find any secrets on his involvement and destroy them, but the both of them are triple agents. Morgan wanted to strengthen the FBC, and used Jack and Terrigrigia as stepping stones. The characters meet up with (possible minus Jessica and Raymond) and the found Jack and boss fight ensued. They found Morgan is responsible and sent to jail, and happy ending!
Revelations 2- Here are some changes, There will be no Moira as a playable character, nor Barry(I'm sorry), None of the stupid ending choices(It makes be mad the way that the handled it), No T-Phobos, and Natalia not being the survivor of the Terragrigia panic. The game would take place in either take place in 2011 still, or a bit before RE6. There are three main characters in this, and I will still keep COOP in this one, it will have the same function in the original. Claire would still keep her role as the offense, Natalia would be the support and warning sign, and there is Steve Burnside! That is right, he is a playable character!! He is in a single campaign, being both Claire and Natalia at the same time. The opening plays the same minus Moira being there or she simply wasn't kidnapped at the party. Claire and others are taken by a group of strange men lead by a mind controlled Steve or Neil wearing a mask, and is taken to...hmm, maybe an Island still or an isolated part of the world like Siberia idk. Neil would still be retaining his role as a traitor but he would have different motives. Anyway, Claire would wake up and is freed from her cell, finding herself in a facility, and is infected with a new stain of T-Veronica. Alex is still the Overseer, and has given everyone a chance to get rid of the virus if they could survive long enough to get the antidote before the time limit expires and kills them. She meets with Natalia early on and takes the role of protecting her, and also meets up with the other members. I they they would survive a lot longer and she would still have that crush on Neil, but that fades over time when Steve enters the picture. Some time after Code Veronica, Albert kept his promise and revived Steve back to life, but not before taking his blood and handing him over to Alex when she was tasked by Spencer to look for Immortality. She still abandoned him, and used Steve to improve the virus for her own plans and she needs the experiments, but needs Steve and Natalia most of all. The girl would be Alex's Daughter(either by blood or adoption) and the plan would either go 2 ways. 1) Uses the virus to make herself a 'Goddess' or 2)Uses her daughter as her Avatar and use the 15 year process along with a mind controlled Steve and together would rule as God and Goddess of the world and is the puppet master. Neil is Landsdale or Jack Norman's son...or apprentice wanting a mixture of power and revenge, and Alex promised them both if he helps her with the plan. He does so, but his jealousy of Steve gets the better of him, and is betrayed because of it, and lead to his downfall. Alex is still the final boss, and it could go two ways: 1)Still that ugly pimple monster, or becomes like Alexia and have 2 other forms. Either way, she is defeated, and Steve is reunited with Claire or he could choose to be a lone wolf but promise her that they will meet again. Natalia...umm...she will still live, but i'm not sure what will happen after the credits lol
RE6- Few things removed from this version. There will no Jake Muller(for obvious reasons), No Neo-Umbrella(kinda), No Fake Ada, No C-Virus, No Helena or her sister, none of the sliding/rolling button nonsense, and no war-torn plotlines. Rebecca is one of the main characters, and she coops with a new guy(Yes, we are going there) as this new dude is a member of the BSAA. Becca is studying a new virus that is popping up, and the BSAA hired her to help make a cure. She is targeted by a terrorist organization, and the NG(new guy) is protecting her while she figures it out. Sherry is sill a playable character, and she is teamed up with Leon as they are still government agents trying to take down this organization after they are responsible for various attacks. I would still keep Simmons as the badguy, and instead of killing the president(He's not in the game at all) He kills an important guy, a high ranking member of 'The Family' that wants to expose their secret society, and Simmons had him killed in the guise of a terrorist attack. He created this new virus as he was inspired by William Birkin to chase his own destiny and he has been using this virus to test what it can do, but secretly wants to take control of 'The Family'. Sherry still has her healing factor and Simmons has turned his infatuations on her and wants to turn her to his side. The only problem with this plan is Leon, Rebecca, and the BSAA. No, his boss fight will not be the same bullcrap of him taking a crap ton of new forms to make us want to break the controller. It will be trimmed down to...two forms? One small, and the other is big. Replacing Carla is another guy/gal who is working for Simmons, leader of the organization as he/she is tasked with making an ultimate weapon to keep the order of the world. He is also given an assignment to kill Rebecca as she is he closest person he knows that could make a cure for the virus. Simmons for Sherry and Leon, and the Head Honcho for Rebecca and NG. The Ultimate weapon is Haos, but is very different from what we got. The four characters would have to work together to beat it, and they win! Rebecca gets the cure from Sherry's blood and happy ending!
RE7- I am unsure if I want to keep the First Person thing still...i'll decide later lol. Anyway, I wanna make more changes. Things will stay the same, but the change will come once the player chooses Zoe instead of Mia. She and Ethan escapes on the boat and instead of killing Zoe, she will be spared and playable and would have to rescue Ethan from Evelyn. She would be on the cruise ship, using stealth to sneak pass the enemies and being plagued by the little girl. At the end when she does find Ethan, she would calcify but not dead as she would still be alive for the DLC. As for Mia....I guess she still could be alive i guess...I don't really care all that much about her. Meanwhile-Not a Hero!! Instead of Chris, Hunk would be the main character as an agent for Blue Umbrella, it makes more sense because he wants to redeem himself, just like Blue Umbrella for their past deeds. It plays largely the same, him going in to try to capture Lucas and try to rescue the other agents. He whoop's Lucas' Candy Ass and all is well. He also replaces Chris in the End of Zoe DLC because it makes sense!!
This is what I would do...i'm sorry if this is long. If you guys have any questions, suggestions or want to further the ideas I have, feel free to do so!