Personally I would like to see an iPhone X with TouchID under the display WITH FaceID. So if I have gloves on or my finger is wet, no problem, FaceID takes over. If I'm laying in bed and holding my phone to close to my face, no problem, TouchID authenticates. It also means I can unlock my phone without picking it up off my desk with my finger.
You would get the best of both worlds and none of the drawbacks.
Plus, it lets the phone not display sensitive notification details until you are the one looking at the screen(with attention detection on, the default, you have to be really looking at it), only then it will display the details(including actual messages, depending on how it's configured). This is great in many scenarios.
This is a tradeoff though, as FaceID doesn't work if you're wearing sunglasses.
I like to be able to unlock my phone when it's flat on my desk without picking it up.