I don't see why they wouldn't release the game on the Wii U. For starters, they're already developing the game with console play in mind, so at most, you're just going to be using a controller and a keyboard, and that keyboard is really just for typing. The Wii U gamepad would put both devices together and eliminate the need for more clutter. Imagine just having a touch screen for typing on the pad, using the gamepad for inventory management and other such things. The experience could be pretty comfortable.

That being said, there are several things that could work against the system's favor, primarily the cock block that would be known as "Wii U limitations"(or rather "console limitations" as the PS3 would be there as well). MMOs like this grow and can do more and more things, which is why a PC that can be continuously upgraded will always win out to static console specs, and make no mistake, the Wii U if anything is only marginally technically better than both the PS3 and 360. If we said the 360 and PS3 used 2005/2006 tech, the Wii U would be around 2008 at best, which is still lagging behind current PC hardware. Admittedly, most PC games have been bottlenecked due to games developed with consoles in mind, but most of those games are static and unchanging anyway. MMOs are quite a different beast.

Second, your idea(and mine ideally) would be to have a Wii U because it takes up less space in the living room, but if you're dealing with an external HDD(why Nintendo can't at least put an empty drive bay in the system for us to add to it is beyond me), then you're dealing with another box and more cables. That kind of defeats the purpose.

Finally, Square-Enix could very well develop on the Wii U(regardless of the "limits" issue), but I don't know that they'd be willing to do so until they see sales numbers and other relevant stats on the system. Me thinks they'll be watching Dragon Quest X very, very closely once it releases on the system, of course there are plenty of other factors to consider like spillover among other things.

Further review is needed.

Until then, you can either buy a PS3(for $250 with a 160gb HD), or you can man up and just set up a PC in your living room on your TV. It isn't rocket science, doesn't require anymore wire clutter than a console, and the game will look better anyway.