With the feature already being so common these days, the most useful and beneficial feature would be to actually try glasses using ARKit. This could even handle sizing if the user chooses to check them out directly from within the app, and of course, the automatic sizing detected by the camera could be overridden by the user manually during checkout if they so chose.
Overall, definitely a novel use of the iPhone X's face mapping. I'm also more than a little happy that I picked the first pair this recommended all on my own :)
