With a decent marketing, it could easily sell more than on WiiU

Doubt it. Who the hell is going to buy this over the dozen other FPS titles that have better graphics and several with monster brand names behind them. Versus Calladooty, Halo, and all that this doesn't stand a chance. 

well according to really old rumors, they said that they might do a multiplat ZombiU 2. That would be a bit more exciting than just a port. I guess they will add some stuff though.

...As opposed to the fake controller that the GamePad is?

I agree, together they might be able to come close to a million but I doubt that even the PS4 version would outsell the WiiU version (at least according to out numbers, which are quite a bit overtracked). It doesn't have to though, it's a late port and everything that's close to 50% of the original's sales will be good enough. (see Mass Effect, Bioshock etc.).

A circa 1997 controller design like the ones PS4/Xbone have doesn't allow for the mechanic of looking down to pick locks or sort through a bag, while glancing up at the main screen to check if a zombie's sneaking up. You would have to change the camera angle with a button, and that would be nowhere near as tense or immersive.

What a waste of resources.  The game isn't good enough for a remake.

This would complete destroy the local multiplayer mode of this game. The game pad is used to create and place zombies around the map

Vita can do the job

Game sucked even with the Gamepad use being really good. Can't imagine what would make it worth playing without that.