Dynamic Playlists

There is a feature I miss from Audion, which they removed before they retired the app entirely, that I have yet to see recreated in any other music player. It was simple. It was brilliant. I want it back.
Basically, Audion used to allow you to group tracks in your playlists into folders, and – this is the important part – check or uncheck folders to include or exclude them from the playlist, temporarily.
Big deal, right? iTunes lets you check or uncheck songs, and you can multi-select and do a bunch at once. Except that it unchecks them everywhere, not just in that playlist, and you still have to do your multi-select by hand every time.
The beauty of this was it gave playlists a sort of dynamic quality: I could have a playlist with folders for happy tracks, funny tracks, angry tracks, sad tracks, tracks with a good beat, tracks with a fast beat, etc. and so on. Then, depending on my mood, I could check, say, happy songs and songs with a good beat, when I’m in a good mood. Or angry songs and songs with a fast beat, when I’m looking to play some first-person shooters. And if my mood changes an hour later, I can uncheck parts and check other parts and it will just keep shuffling through whatever is active when it comes time to pick the next track. It was brilliant.
And I miss it, and I want it back. iTunes doesn’t do it, WinAmp doesn’t do it, Songbird doesn’t do it, VLC doesn’t do it… nobody does. And it doesn’t seem like it should be necessary to write an entire music player just to get this one feature; maybe one day I’ll get up the nerve to modify Songbird or VLC to do it. Or maybe, sometime between now and then, some kind-hearted developer will hear my pleas and implement it in their player. Who knows.
If anybody out there knows of a player that does have this functionality, please, let me know in the comments… I’d be forever grateful!