I expect for RE8 that they will continue the same kind of theme from RE7, and I think it will have a similar progression to RE1-RE2 i.e. a bigger city-like setting, more enemies (hopefully) and more of a deep dive into the company that Mia worked for. It'll probably stay first person for the next couple of games as well.
I think that they might use a main character that we have seen before, hopefully Jill if they do, but another part of me thinks that Capcom will see the new numbered games as a way to move on from the earlier games by using all new protagonists. Even though the RE fanbase had very mixed reviews when it came to Ethan and Mia, I think the majority of newcomers and casual fans who enjoyed the game didn't really care about who the characters were, as long as it was a solid horror game and that is probably what Capcom will take into consideration. They know that they will keep us happy with the inevitable RE3 remake and I expect we will get a cameo even if they aren't the protagonist.
One of the main that I need to change from RE7 is Chris's model if he comes back in RE8. I's just so bad I can't get over it, and we've seen how they can find fairly similar models to the characters when we look at Claire and Leon in RE2. I also never want to see Mia or Ethan ever again... I might be ok with Zoe.