No answer to this yet? 😉
My comment: when adding playlist folders, this may get a bit different since playlist folders may be empty playlists just containing all entries from sub-playlists. So I’ld delay this feature request until playlist folders are available.
After that… I’ld make it an option only, because showing empty playlists can be useful at least for debugging (if the playlist vanishes, is this due to a bug or due to the fact that it’s empty? 😉 ).