That's the thing. Every phone more or less has made it a point to be in s big single button on the front at the bottom, it's exactly where we all expect the new Ines behind the screens to be!
Sticking it on the back in the middle is bad enough and unfamiliar, sticking it next to the camera is lazy and cheap and useless.
We'll have to see if AR takes off, it hasn't yet. VR is still dead too, people don't like these things I guess we don't see them as useful, like 3D with it's huge push from the manufactures, tons of TVs with it, now because no one cares or likes it they are making less and less and shifting to 4K or HDR etc.
So it's by no means a guaranteed success. And I still suspect people would prefer better photos and videos then AR. I slo don't believe many use iris scanners, because finger print sensors have been so dominant. But Samsung have put it in a few phones now so some must like it?
Not sure why you're repeating what I'm saying. Yes it's better to have the fingerprint sensor on the front.
I said nothing about VR.
There's no indication that 3D cameras would result in lower video/picture quality. The cameras would still work as normal cameras.
If the iPhone 8 rumors are true, it'll be more technologically advance than the S8 by a long shot. That's not even taking the A11 into account. It'll have the power of an iPad Pro in your pocket.