I wouldn't change the main console and clearly Nintendo probably aren't keen on investing money on a re-design but I would change the gamepad.
1. I would turn it into a very attractive and decent joypad not unlike ps4/xbone but with a small touch screen display. I would put analogue triggers in even if this puts original gamepads at a disadvantage but perhaps remove the near field chip reader. They will just have to use a different control layout for certain games on older gamepads with analogue triggers.
Considering the wii u is weaker than 360 and PS3 in many ways I don't see how it can have a future at a price other than budget.
Whatever happens this is a self-inflicted wound. Nintendo made some utterly stupid decisions and they deserved this failure. The specification to price ratio of wii u at launch was an utter joke. It's fair to say the ps3 and 360 have a far larger selection of technically impressive titles than wii u. For those who argue that the wii u's technically better games will come later I would just make the point that a console released in late 2012 with a fairly high price tag should easily outperform dated consoles from 2005/6 day one. The fact the wii u can't do that shows the utter contempt Nintendo has for its end users.
That said I'm enjoying my wii u but I just feel technically its an utter embarrassment to Nintendo.
