The YouTube app on Android P Developer Preview 2 seems compatible with the gestures on the fingerprint scanner: in particular, some observe that with a tap on the sensor you can make a superimposed menu appear with the playback controls.
There do not seem to be other actions, at least for now; the swipe down continues to call the notification curtain. But it is easy to imagine a side swipe to go forward / backward fast, for example, if the idea takes hold.
Availability is not very clear either
The thread on Reddit reported below is the main source of information, and the opinions of users are conflicting: the Pixel 2 family seems to be the one in which the gesture is more likely to work, there are fewer certainties about first-generation Pixels and none information on other smartphones that can install beta firmware.
It is possible that Google is proceeding with some server-side activations to test user acceptance.