Currently Online 
The most unrealistic possibility I could think of:
Ultima X
(exclusively on WiiU, surprise announcement at E3, development started years ago, supervisor: R. Garriott)
Now this would be a sensation and interesting in different ways. PC-only gamers would be extremely excited and enraged at the same time, even those who never played an Ultima game. Most of the PS3-only or X360-only owners would get mad even though many of them have never heard of the Ultima series before.
A bit more realistically:
A well-done WiiU port of Civilization V, Anno 2070, a Total War or The Settlers game, or the upcoming XCOM remake could be a great addition. Or how about a new SimCity with real devotion in development (it would be about time...). Generally western TBS, RTS and economic sims.
Still my secret wish (which it already was for Wii):
Point&Click developers port their best adventure games to WiiU. Unfortunately this won't happen as these developers are generally very narrow-minded, with the exception of Telltale - the only relevant modern p&c company which has understood the importance of releasing games from this ever-struggling genre on multiple systems.
Generally I'd like to see more western support on Nintendo consoles outside the annual standards like Fifa/Need for Speed and all those already-available-on-multiple-systems HD FPS/TPS/Action games. I hope we will soon see more interesting western announcements than Darksiders 2, The Darkness II or Darkwhatever 2 for WiiU.
