I have a list of games that are pretty much obvious, however, I do have a different list of games that I think SEGA should remake/port because it might seem feasible.
Here's one of them:
Shining Force: Return of Dark Dragon - It's already a good remake of the first Shining Force on GBA. Port it to Android and iOS devices. It's a slam dunk.
I think THQ had distribution dibs on this game, but since they went broke, I'm sure SEGA can scrounge up whatever's left of that.