What I believe is Nintendo's remastered game for 2015.....

[Maraccuda]

Soundwave said:

I could see it being Mario Galaxy HD 1 + 2 or maybe even a full blown Mario 3D All-Stars (with Sunshine and 64 in as well).

If Zelda U suffers a delay then something like that could at least sorta fill in, my guess is in that scenario, Splatoon would also be moved into the fall.

Perhaps Xenoblade HD (literally just the Wii game but running in 1080p, no other changes) could happen as a bonus disk with Xenoblade X, but I don't think Nintendo will make a big deal about that, much like Bayo 1 being thrown into Bayo 2 as basically like a bonus. 

"Remaster" implies something more like Wind Waker HD. 

Mario Galaxy HD collection is a safe bet too. But if so it would feel like Nintendo have saturated the Wii U market with Mario platformers lately.

I still wish the Mario Anniversary game on Wii included more than just the 3 NES games, but it is another possibilty.