So, if you're carefree like me, and have your screen lock set to 'None': Ambient Display does not work. After setting a lock screen, it works now -- not very well, but better than not at all!

On my Moto X, I treated the power button like an 'unlock button', since the active display showed a lock screen on nudge / de-pocket. If you happened to do this too, that's not going to work on the 6P. Sorry!

Also I said I'd try a couple 3rd party apps for active display and report back:

• AcDisplay: More or less the same as Google's Ambient Display. Also does not work without a lockscreen, but you can set it to be your lock screen (still locked when you press power, though). The unlock animations messed with my widgets a little.

• Gravity Screen: Really good at first. Tons of options, sensitive. Too many options. Lots of edge cases. Works without a lock screen, but jumps straight to your homescreen when nudged in this case. Has a rather aggressive default timeout (10 minutes) after which it doesn't seem to respond to nudges or anything. Setting this to a longer timeout drains battery. Oh well. I think with some tweaking and developer feedback, this one could work out.

Thanks for all the suggestions!