There's a concept I like in there somewhere.
What happens if you hide a track from the track pane, then hide it from the mixer? How do you get the track back again?
If you compact a folder track, the individual tracks reduce to a 3-pixel high track lane. make a folder track with clips in the tracks, and click on the folder picture where the track number should be. It looks like this:
https://stash.reaper.fm/oldsb/1157558...ultiselect.png
Is that small enough? Or do they need to disappear completely?
I already have a BR/FR for these mini-tracks to show better in the TCP. Currently they show selected or not, but are otherwise invisible:
I guess if they never have clips in them there's no need to show even a 3-pixel lane, but I'd use this for tracks with clips in them too. Sometimes you're just done with part of the mix and don't need to see the track or its mixer, you just need it to play. If I could shrink tracks to that mini size selectively, that would serve nicely.