Stardock is working on a "not MoM" (Master of Magic) that I'm really looking forward to. My personal list though, would be...

Remake Independence War 2, the best (IMO) cockpit-level PC space game, but do a new version with an open-ended Elite-type trader universe instead of the linear scripted plot in that game. It's the only space game (other than Elite) that has even tried to get the physics right. Either that, or turn Orbiter into a combat sim. I'd buy that.

Red Baron: Doesn't anyone want to fly and fight at short range in fragile kites with guns, instead of missiles? Or are combat flight sims just totally dead now?

Speaking of which.... what happened to helo sims? Would nobody be interested in a new Longbow/Apache sim?

Populous would be fun to see as a new version.