I'm curious to see how reliable an in-display FPS is, and the speed of it. Could be slow in the early days. I prefer the FPS on the back vs any other form of biometric security to this point, so it'll have to be really reliable and reasonably fast for me to jump on board with the idea. Are we sure of the security of it? It's easy to say it's actually registering deep data of a fingerprint, but it's not out of the realm of possibility that it's using a less secure form of registering.
I have a gut feeling that if Apple unveils a second-gen of Face ID that is vastly improved, this push to go with an in-display FPS sensor could fall by the wayside, at least at the top-tier.