I think they should make different sub-scenarios in each part of the game. For example, in the RPD, in the firs part, you can play as Claire or Leon. in the second part, you can play as leon or Ada, etc... And Ada should only appear when Claire and Leon are nott together.
Also, i don't like Ada looking like a spy, Leon is supposed to believe she is a civillian. Unless she finds the equipment somewhere in the station. It'd be nice to play as Ada when she is not wit Leon, and watch her messing up with Anette, tring to get the virus, and later, what happened when she woke up and escaped from the lab, which should include her throuing the RL to whoever fights the tyrant in the end..
In the CVX scenario, Wesker should be playable, looking for alexia. After Steve was captured, Claire should team up with Chris until the end of the scenario. Alexia should appear more, and not return to normal after she mutated once (nor Steve)