Ideally, I wish NRS would be able to come up with someone with extra defensive options worth using. Of course, there's an inherent issue with such designs in fighting games, so it's not very likely that we're getting such a character.
A toolbox-y type is also welcome. For example, something like Aganos from KI or, failing that, F/T from MKX, although that's probably stretching the definition.
In terms of particular characters from MK franchise, I've looking forward to Raiden and hopefully Shang Tsung, but I'm not quite sure they will be anything I've described above. Although NRS themselves, I feel, aren't sure what they want from Raiden, but hopefully not something like TG Raiden from MKX.
I'm somewhat curious about some other characters, like Jade. We'll see what NRS will show us.
Also someone using some down-to-Earth style would be cool. I've expected Kano to fill this niche in MKX, but even his MK9 incarnation was more fitting to that description.
Hoping for Mileena to come back. I know I know killed last game bla bla bla, I will keep my fingers crossed until the game launches.
I'm afraid she'll have to sit this game out. But personally I wish we'll get Shang for him to uncork his (presumably existing) stash of extra Mileenas.