I recently finished "Perimeter" a quite unusual rts with great story and deep sci-fi atmosphere. But it's buggy as hell. I think that if a remake that would fix issues and made a better integration into steam (like search for multiplayer games and workshop) that would be very cool.

I would love to be able to play Blade Runner again. It sucks that because of those lost assets a GOG release is pretty much impossible. But man, just imagine what this already excellent game would look like with completely revamped graphics (at least as far as the characters are concerned).

I would love to see either a remake or remaster of Warcraft 2, the only changes being new graphics/audio/video/sfx, high res widescreen support and similar aesthetics, and possibly some user interface enhancements to bring it more in line with much newer RTS games with hotkeys, command groups, waypoints etc. They appear to be doing a remaster of Warcraft 3 and Diablo 2, however I haven't seen any substantiated claims on a Warcraft 2 remaster yet, but hopefully they decide at some point to do that as well.

Emperor of the Fading Suns

The gameplay is a bit Civ meets Master of Orion
The Setting is a lovechild of Warhammer 40k and Dune with a few bits of Star Wars sprinkled in.

The same 20y old thing remade with modern graphics and not that bugfest the original was would be a dream.

Heretic
Clive Barker's Undying (or at least a sequel)
Stunts
SimCopter
Transport Tycoon (Locomotion was disappointing)
Star Wars: Jedi Knight