I wonder whether Nintendo actually can do that, despite being pretty sure they won't. The thing has only one port, namely power port, and that's it. You cannot put data through the power port. Well, you can, but you have to think about this possibility before assembling the controller.
I don't actually think Nintendo will create any widely available wired solution. What I find probable is somebody finding a way to replace BT module of Pro Controllers and Wii U with something using wires. That said, this doesn't sound like something you would like to do to your devices. So, I assume, organizers of large Smash-oriented tournaments will mod their Wii Us and controllers (this would by the way make them unusable with normal consoles - profit?), and everybody else will stick with wireless.