The platform of choice I'd prefer to play it on would PS4 personally as its a nice middle-ground PC and Console (plus it allows remote play with the Vita and I've always enjoyed the thought of a Banjo Kazooie style game on a handheld, where the 3DS is too weak hardware wise unfortunately). I understand there is a legacy to somewhat hold with Nintendo customers, and whilst I certainly don't think you "owe them" or anything like that it is a nice little narrative if Project Ukelele ended up on a Nintendo platform (whether that be the WiiU or a successor depending which is relevent at the time).
Also as an aside as I've seen the discussion going on this thread already, I find the notion that if a WiiU fan and a 3D platformer fan are mutual exclusive is a false assumption, as I think people's taste naturally evolve over time and expand to take on many new experiences (especially when one such niche like 3D platformers has been such undernourished for... years) but that doesn't mean the adoration has diminished. I assure you Project Ukelele will sell just as well on other platforms and probably better considering the built in audience, that's not any kind of slight towards the platform, just stating facts, a lot of people grew up with this style of game and it deserves to be played by everyone if at all possible (ie. see how well Hat In Time is doing currently)
So personally for target platforms I would shoot for PC, PS4 personally. I understand if WiiU has to be in there somewhere because of fan demand, but please stay away from the weaker end (360, PS3, 3DS, iOS etc) if at all possible as to have the least amount of restrictions on the design and hardware running behind the game. Honestly whatever platform it ends up on it doesn't matter to me as I own virtually all of them, I just want the best chance for this to succeed to see the rest of the "Playtonic Cinematic Universe", and in an ideal situation I want it on every platform so people can choose to play it on their platform of choice and have it available to literally everyone possible; that is my concern, not any console wars or any crap like that.