Allow multiselect->delete from playlists
Currently it's far too painful to select each video individually, select Delete, confirm, repeat. Alternatively, a "Remove all watched videos" from the Watch Later list would satisfy my needs.
Done. Should be working. It is working on a timer, so it may take a while to delete large quantities of videos from a given playlist.
Steve Dower commented
Doing the same as for adding multiple videos to a playlist (which is much appreciated!) is fine. I don't mind waiting (sure others don't either, but can't speak for them) but the repeated interaction is annoying. Though it would also be nice for both to work in the background.