Two buttons that have become very important the past 2 gens in gaming are the R2 L2 buttons but it seems they aren't there to keep the console lighter. But we have the touch pad so will that be the interesting replacement of the R2 L2 buttons. 

for example in Call of Duty it is the Grenade and special grenade button but for the ngp it could be an flick on the right side for an grenade or the left for an special. and different taps, flicks and movement directions for the type of throw 

just make a arc on back touchpad or use front touchscreen

Since it has a touch screen this can be very easily changed. e.g. instead of pressing R2 to throw grenade flick finger forwards on screen.

For me, no need. The inclusion of touchpad, touchscreen, and six-axis  = endless possibilities

Not only in both screens, there is even the motion sensor that can be remapped for some controls.

The possibilities are endless if we compare it to PSP

Very very true ^^

Grenades suck in Cod anyways lol