Ultima Worlds of Adventure 2: Martian Dreams.
I'd say the Ultima franchise as a whole should make its glorious comeback (Shroud of the Avatar wasn't quite what I expected, sadly).
Yeah, it would be awesome if the Ultima franchise came back. But considering EA owns the rights... let's just say it'll either never happen, or if it does happen, you'll wish it didn't.
But hey, we can still dream.
It'd be nice if Might and Magic made a proper comeback as well, Sci-Fi mixed with High Fantasy and all.
I'd like to see Wizardry come back as well.