About that new map:
A cool idea would be a map that has some kind of randomization each time you play it. Rooms could be different, task locations switched, or maybe even the starting point is moved to a different spot.
Another idea is a map literally split into sections, where the only way between them is a portal or some kind of contraption. (I personally love the idea of getting flung between the areas with some kind of catapult. xD)
As for players themselves, a neat thing could be a visual sign of who's an imposter (or crewmate) that's very subtle and only shows up for a split second (and also is kinda rare to happen). Something like a tinted glint on the face shield could happen. (Impostors would have a tint with an ever so slightly red tint which you would have to be paying close attention to notice.) (This could apply to Ghosts too, somehow, like them becoming partly visible for a brief second on occasion.)