I think the Touchpad could replace the Vita's rear touch panel, but the front touchscreen? Not unless you add an actual touchscreen, which will never happen.

Besides, the Vita used as a controller for the PS4 has far more potential.

I also think this could be due to Remote Play compatibility. To make the Vita a DS4 controller.

Yes, as I said. It's easy to port games that don't use the touch screen in any innovative way. But for that you don't need a touch pad on your controller. You can port those games on any controller. And the back touch pad is very limited as well. Not only because it's hard to interact with with your fingers but also because almost no game uses it. Again, very easy to port on a controller without a touch pad.

The only thing the touch pad on the DS4 does is emulate buttons with gestures. So far I haven't seen a game that uses so many gestures that you couldn't map it to individual buttons.

Just an example:

Gravity Rush - Uses touchscreen but only as a replacement for more buttons. Easily portable on any controller.

Murasaki Baby - Uses the touch screen as core gameplay element. Impossible to port on any controller, even with touch pad.

And now it's your turn to name a single game that can only be ported to a controller with touch pad.

There is nothing a touch pad makes possible or easier than a normal controller with just buttons. The only thing it does, is make controls more interesting for people who can't deal with many buttons.

Not a bad theory, but my guess is that the DS4 was already designed with touchpad long before it became evident that the PSV was becoming a stagnant platform.

Undoubtedly, the DS4 was designed with the idea in mind of having a level of PSV compatibility when designing PS4 games that have the option of using the PSV as a controller/aux display, as well as for Remote Play, but this is definitely not the same as designing an input device with the prescience that their brand new portable was a dead platform before it even had the chance to develop a software library.

What? The Vita had no games. How could the DS4 have been designed around playing something that doesn't exist. Can... not....compute.

Its like the REAR touchpad, gimmicky. but its there if they ever want to port something.

what is the point of the rear touchpad even? its not even easy to use.

Wrong.
http://www.gamespot.com/videos/tearaway-ps4-demo-sony-press-conference-gamescom-2/2300-6420791/

just listen 50 seconds

You did be surprised... try something. if you have a smartphone, put it in your hand, then open an app or something atht will allow the onscreen keyboard show up. You know, what you type on. Now look at the area that keyboard covers, you will find that its practically the same size with the PS4 touchpad.

Basically, if they had made a monochromatic screen... like black and white or something that would have allowed a keypad appear if you wanna type or very basi game information like helth and ammo count or a map it would work perfectly. I am not talking about a screen to use for remote play.

Sooo... like the Dreamcast screen, but with touch controls?

This would be a lot more aesthetically pleasing, though (but probably sadly impossible)

Probably. Never really understood the use of it.