I do agree that FaceTime itself will be perfect, I’m just not sure if using it will be more convenient than TouchID. Unlocking your phone technically takes two actions...look at the phone, then swipe up. Currently, and (on the 8/+) all I do is press the solid-state home button. Just one fluid action.
Also, this could have been my perception, but it doesn’t seem instantaneous. When Federighi did it on stage (and in several hands-on videos I’ve seen) it looked like their was a ever-so-slight delay, so really, you have to 1. Look at phone 2. Wait for unlock 3. Swipe up.
I could be wrong. I hope I am because it’s a great concept. I just want to see how it works IRL.