This way, private torrents could “escape” into the wild, still maintaining the privacy and social/closed community effects of the private tracker.
Except that it wouldn’t. The infohash that the private flagged torrent generated is different vs a public non-private torrent of the same contents. Your suggestion would purposely share the same exact private torrent infohash into public DHT/PEX, that would certainly get people banned at the source private tracker(s). I also suspect most/all torrent client developers would consider that incorrect behavior.
If you wanted to do a more “correct” approach on this - Create a brand new public non-private flagged torrent of those contents, which would generate its own unique infohash, then it’s just a regular torrent. You’d end up needing to seed multiple copies of the same torrent (the original private flagged torrent and your new public torrent) but sure that would be possible as long as the torrent client itself has DHT/PEX enabled. Most private trackers won’t care too much but some of that does depend on individual trackers and uploaders, you’d need to check their rules.
Not overly active but you could sub/participate in
!opensignups@lemmy.ml
!opensignups@noworriesto.day
Also !torrent_trackers@lemmy.ml (it’s more of a tracker listing community)
And right here in dbzer0 there’s !trackers@lemmy.dbzer0.com for general discussion as well.
EDIT: For specific sites / non-Lemmy you can monitor https://opentrackers.org, I kind of wonder if the admin ever made it over to Lemmy. On Reddit he goes by cuddlebunny and an earlier nick IIRC (but that’s all ancient info now probably).