Would they pull a Twilight Princess and release it on both consoles?
Can Zelda Wii U be made into 4K?This is actually a tough question, it's not a case of just up-scaling the graphics (their would be no point in releasing the game again). However they may not need to actually redo the graphics by much. You see develops usually make the graphics at higher resolutions then scale them down for the console, so it is possible they already had 4K ready graphics to start with. However this is also just hopeful thinking. While developers usually make higher resolution graphics and then scale down, it is not always the case and it doesn't mean the graphics where originally made in 4K.
There is more to it then just textures as well. The models could also be given more polygons to look better but this is not really necessary as models on the Wii U already look great and this would allow the console to save it's power for other things.