Neither of those would have a big impact. I see only two things that would make Wii U take the sales lead (or come close)
1. A steady stream of interesting titles like DK, MK8 and SSBU, a new IP that creates buzz, big promotion for X and a price cut mixed with a bit of a drought for PS4 and no price cut for XBOne. All of these things have to happen together. I guess a new IP that creates buzz could do it alone, but it would have to be quite the interesting game.
2. Nintendo buys controlling interest in a 3rd party (or 2) and brings their titles exclusive. I mean a major third party, like Capcom, Square or Take2 that has some significant titles with dedicated fans that will buy a system to play it. If, for example, Mario fans AND Final Fantasy fans were buying Wii U's to play their favorite games, the base of users would grow to a solid number and other 3rd party support would likely follow too. This scenario is unlikely.
I don't think Pokemon or Metroid would have much of an effect. Only one drastic move or many consecutive successes will turn things around for Wii U.
