If you took away the controls, it would be a pretty unremarkable TPS Horror game. It'd still be entirely functional, but it would be bereft of an identity.

I have to agree with some of you, the gamepad indeed does add a different feel to the game. I don't think I would like it without it.

Not only for inventory, but when shooting turrets and sniper rifles, the gamepad was pretty handy with the zoom and the motion controls to move the reticle around fast.

You'll just have to take the dozen or so people in this thread that have had the experience at their word (myself included), the gamepad adds to the tension and like others actually adds to the immersion for me, rather than breaking it. 

The ps4 controller has a touchpad and there is remoteplay with vita which could be supported maybe

A touchpad won't cut it. Vita support would do the game justice if they implement it correctly, but then that would open up a whole new can of worms in terms of marketing because they would have to try to target the audience that owns both a Vita and PS4 and that's just a mess in itself. And then the XBO version would be screwed either way, and so would the PS4 owners that don't own a Vita.

I just don't think it's a game that really works on other platforms naturally.

Nobody's going to care, not only was it "not really requested" for porting like Bayo2 or something, w/o touchpad it's not only going to be difficult to differentiate and implement correctly unless they harness a new gimmick, its going face super heavy competition from AAAs on PS4 and XB1.
Reasonable conclusion: It would still sell more on Wii U then on XB1 and PS4, possibly even combined.
As for whether it is worth it that depends on how much money they spend on vs how much they make, clearly they want to sell more, and are thus expanding there market.
Assuming confirmation.

Not in the same way though. Using the separate second screen physically recreates the scenario of doing one thing while having to look up to check you're not in danger. A workaround like pressing a button to change the camera angle would not be the same.

O: Isn`t there the Xbox Glass, or something that they mentioned some time ago...? I guess that could work maybe..?? Though these alts seem kinda messy to get everything needed just to enjoy it.

That's possible, but like you said, it would be a bit messy just like the situation with the PS4 and Vita. It's just not a game built with these platforms in mind. It would be like putting Wii Sports on the Xbox 360 (before the Kinect came out).

But can the PS4 and the X1 handle the Wii U graphics?...