I think DQXI will be PS3/PS4 only. DQH is not releasing on Wii U, so I don't see DQXI going there. I also don't see 3DS as an option due to technical issues: it would look and run like crap (DQVII already runs pretty poorly on the system with a bad framerate and lots of pop-in, and it has rather simple graphics/assets), and n3DS-only would be silly because the userbase will be relatively small. Maybe they'll do some garbage streaming online-only version like DQX 3DS, but that's probably all we'll get on the 3DS, if anything.
I don't think they'll bother with a Vita version as you can just remote play the PS4 version, and the userbase is too small.
I don't think they'll bother with a Vita version as you can just remote play the PS4 version, and the userbase is too small.