It wouldn't outsell the PS4 version, could outsell the X1 version but I'd doubt for a simple. Obviously theres an audience on the system for this game to do like 2-3m on the Wii U easily (more so then the X1 audience). Problem is most fans, even if they had a Wii U would get it on PS4. I mean if you want KH3, you probably want FFXV and probably certain other Japan PS4 games as well which means getting a PS4. Once you have a PS4+Wii U then you're not going to pick up KH3 for Wii U are you? So in actuality I think it'd just about pass 1m, not through lack of interest but through the PS4 version cannabalising it.
If it came out today this wouldn't apply so much, but the game won't hit shores till 2016 at the earliest.
Unless Nintendo is funding the port it won't happen though. Square are not going through all that effort to port it to Wii U when anyone who wants the game is going to find it anyway. Thats what system sellers do, they make people buy the console the game is on







