Mojang is too busy
Despite having no interest in playing ports of Minecraft on new platforms, plenty of others are eager to do exactly that, and I do think getting this piece of pop culture on Wii U would benefit Nintendo. Every game matters. And considering the GamePad's functionality, it'd also likely be a worthwhile version of Minecraft in its own right. But such a port isn't happening -- not yet, anyway.
A recent tweet by creator Markus "Notch" Persson covered the topic: "I agree a Wii U version would make sense, btw. The only reason for no current plans is we've got too much work already. I <3 Nintendo."
I don't doubt that the studio is busy. I also don't see Minecraft losing significance anytime soon. As such, I think this will be something for Mojang and 4J Studios to look at again down the road.