I think Resident Evil 1 might feel quite slight now by todays standards, and it would be a good candidate to add in some extra game modes to aid longevity.
I've always enjoyed zombie hordes in games like Days Gone, Dead Rising, Left 4 Dead, and although Resident Evil has dabbled with Mercenaries it's still only a dozen or so zombs at one time. It would be pretty cool to have a proper horde mode in a Resi game.