I recommend using the "Open With" extension with mpv. This allows you to right click on any sort of video link that youtube-dl supports and launch that link in mpv. mpv has a "stay on top" feature that can be enabled by default when mpv is invoked in this way. The result is picture-in-picture that supports virtually every video site on the net.

Happy to tell you that PIP functions if you enable in in config!

PIP is a good point, not supporting play/stop via Bluetooth is another for me personally.

it does though, at least in beta