More relevant, I think, is the UI.
Forget the exact technology, TODAY we have a UI that is pretty well optimized for two tasks.
You can just pick up your phone and the lock-screen widgets tell you a bunch of immediate info (new emails, notifications, SMS, etc). You can then touch the home button (without even pressing, if you've set preferences correctly) and swap to the "unlocked" phone with whatever app you were last using.
Bits of this are less slick if you have an older iPhone, but with an iPhone 7 all the pieces work seamlessly.
If you now add some sort of face/eye recognition to the mix, you lose any value to widgets on the lock-screen because there'll be no "normal" way to view the lock-screen without immediately unlocking. (On iPhone 7 this is not a problem --- view the lock screen by picking up the phone. On earlier phones, either view the lock screen by hitting the power button, or by hitting the home button using a non-fingerprint finger.)
I'm not sure this is a useful direction. I think most people (especially with an iPhone 7) find the lock screen widgets crazy useful, MORE useful than some sort of immediate unlock would be. And I don't see a UI that achieves that same goals (show "updated status widgets until I want to switch to 'unlocked phone mode'") that's simpler than what we have today --- making that switch from "status update display" to "full phone with apps" mode has to have some sort of user touch.
The only way I can see this being valuable is something like:
I look at the phone but it is NOT immediately unlocked. Instead it remains locked until I touch something. This would allow for "traditional" (touch the home button) unlocking, but would allow for ONE slightly more slick move, namely when I swipe say an email or a text message, I immediately get dumped into the unlocked app without having to move my finger to the home button.
This is one of those tweaks that you can live without, but would be cute to have. My guess is that's how Apple will do it, and as a consequence, it won't seem like much of a change at all from the way you use your iPhone today, except for that one small usage change.
(And note, Apple could achieve the same result without eye/face recognition if it used ultrasonic fingerprint recognition that works anywhere on the screen. This technology exists and has its own value --- eg it can also be used to provide 3D-touch style pressure sensing. To me it seems like a more elegant overall solution than adding eye/face recognition.)