Currently autoplaylists allow an autoplaylist to be limited by track plays, how recently the track was played, when the track was added, and rating. However, there are other metrics that would be useful to limit inclusion in these playlists by - total album plays, and BPM, are two possibilities that spring to mind.
Therefore, the ability to limit the number of tracks/albums included in an autoplaylist by any numberical metric, rather than the ones currently given, would be really useful.