Nintendo needs to sell this 'next gen' marketing at full force for the Wii U. The only way to see it move units at a good rate is to value and price it at $249 w/ NSMBU+NSLU bundle and a 3DW bundle (coupled with the 'next gen' marketing). Make similar bundles for DKCTF, MK8, and SSMB when they release (and future big releases such as Zelda).
It would eat into their profits for quite some time but I think it should pay off in the long term, not to mention keeping a healthy market share assuming PS4 and X1 track higher than it for some time as it looks to be that way (at least for PS4).
Gaming on: PS4 Pro, Switch, SNES Mini, Wii U, PC (i5-7400, GTX 1060)