IssueTracker

If it were not for NFC unlock I would not use any kind of display lock at all.
Face unlock does not work properly, as well as trusted places.
Bluetooth would not make any sense, since I would have to unlock my phone to switch on bluetooth to have my phone unlocked by bluetooth (wtf ?).
On body detection is useless, too: whenever I carry my phone around in my pocket with the screen unlocked, all kinds of strange things happen when the screen gets activated by some app or another.
As for fingerprint, my phone does not have one. Even if my next phone had a fingerprint reader, it would be of no use when located in the back and the phone is sitting in any kind of holder or cradle.

We have passed this to the development team and will update this issue with more information as it becomes available.

@3 Please do consider re-adding this feature.
There are actually people who think it's an awesome thing to have. Even medical cases, such as this one:
https://issuetracker.google.com/issues/65425413#comment37

Bring back NFC unlock. Or add NFC U2F unlock with something like Yubikey.

Another thing I would like to see is custom Smart Unlock providers. This way a company like Yubikey could add support for NFC U2F dongles.

It was really useful to me, I had a nfc tag near my mouse pad. It was safer and much more precise compared to gps location!

I have found a workaround, though it requires root and manually editing a preferences file.
Details on pastebin: https://pastebin.com/2RSZzERg