• Drop an album from a folder on disk into the playlist
• Select "Move to collection" from the context menu

This works great! It would be even better though, if the entries in the playlist get updated to the entries from the collection after moving.
Currently they are useless, as they point to the filesystem where the files got moved away from.
So I manually have to open my collection view, search for the album there, drag the album into the playlist and remove the old entries still pointing to the filesystem.