So I would love to be able to set some kind of "schedule" on the play list updates.
This could take different forms:
1) "Pre-compute Schedule": my PC stays on all the time. So if I normally sync when I get home from work at 6:00, pre-compute the sync set at a given time (say, 3pm) so it's ready to go at 6
2) "Update Schedule": for each Playlist, indicate how often I want it updated (once/day, 3 days, week, month, etc.). Thus, I could have my fast playlists update frequently (every sync), while my complex/slow ones only once a week or month.
This would be even more appropriate if each playlist was bookmarked on a device (i.e. if my phone would keep track of which track it's on for Playlist #1, vs. which track it's on for Playlist #2, etc.). My most complex playlist (not longest, but most nested) works out to ~2,200 tracks, so it takes me weeks to play through (i.e. before I would need it updated).
Another way this could be done is as a percentage change: i.e. if the tracklist was X% different than the last time. However, you'd have to compute the playlist repeatedly to test the condition - unless you added "Pre-compute Schedule" as above
Other performance ideas:
"Metadata Only Sync" - THAT I would use with "auto update on connect", so that the "Last Played Date" & Count were very current. This would make the "pre-compute" much more accurate.
"Network Metadata Sync" - since Metadata is lightweight, it could be sync'd over the cellular network. This would make "Pre-computing" the sync set almost perfectly up-to-date if it were scheduled automatically. Or, the network metadata sync could trigger the re-computing of playlists...