nice ideas nick. i'm surprised gangs of ny was never made into a game.
maybe even harlem during prohibition. that era hasn't been touched at all.
only other thing i can think of is place the story 20-30 years into the future.
but the setting and characters arent really the issue, its the missions and gameplay. there was absolutely zero evolution from 3 to 4 aside from the multiplayer mode which is treated like an afterthought.
maybe a gta where the main character is a cop who eventually works his way to undercover narco. idk something new.