Maybe I'm not understanding, but you can already set a playlist as a rule for a smartlist. So if it says "Only in playlist A" then playlist A defines the set of files for other rules.
Be
very careful with these rules.
It breaks if you make any changes to them while a Client copy of MC is connected. The client copy can just be connected and sitting idle, but if they're open and connected, when they sync changes, all uses of the nPlaylistID (which is how the Playlist is any X rules work) will get borked, and the Playlist rule will no longer limit the Smartlist.
If you're using these to do anything "auto" (like deleting or syncing) this can cause badness, in some unlucky cases dumping your entire Library, or a good portion of it, into the Smartlist in question.
As long as you make sure ALL clients are closed before you make any edits to the Smartlist at all, then it works fine. But all you have to do to bork them up is open the Edit Smartlist dialog and click OK to it (instead of Cancel) and, if a client copy of MC is connected, the Smartlist will be borked in a few minutes.