I would imagine if you map clicks to ABXY then you wouldn't map another function to a click. Although I'm guessing (and this is just a guess) that you can actually map five different clicks to one trackpad. Four on the sides and one in the middle. Not sure if that would be optimal though. Can't really think why'd you need 5 clicks per trackpad.
Ah, should have thought of that, that's a pretty obvious solution. I then thought about how it would move you around if you swiped up to the click zone, but obviously you'd take your finger off first, lol.
By the way I could see use for a middle fifth button - use it like the click-in for analog sticks, for things like a quick melee/knife attack up close. Your finger is always around there, so it's super quick to do.
Thinking about it this way, I can see how it would be faster than moving to the dedicated buttons. With a little learning curve, it could save those precious fractions of a second in competitive gaming.
Wish they had a concave top for the analog stick, or even the hybrid approach of DS4.