Really good question. Japan is keeping Vita alive, the only potential system mover in the west, afaik, is going to be Borderlands 2 and from the footage I've seen, it only looks okay.
MK8 and Smash will do great for WiiU but I wonder if they will be enough to get the WiiU ahead of the Vita this year. IMO the fall lineup for WiiU doesn't feel like they will move many consoles.
I can't really speak to the fall lineup for the XB1 since the games supposedly coming out then, I've seen very little in the way of gameplay or story.
I'll guess that WiiU will catch Vita before XB1 catches WiiU. They could very well happen around the same time. WiiU has to sell 2mill on top of w/e Vita sells which means XB1 has to do 4mill on top of that.
Anyway, E3 is definitely going to be huge in deciding which will win this particular race. I'm hoping for great software for all the new consoles and handhelds.
Edit: I'll add that if WiiU does pass Vita, it probably won't hold that lead for long. Vita will likely get support longer than the WiiU. Look at the PSP.
