BaconBits was a Reddit tracker with a maximum user count around 6000. They eventually closed because most of the users could get the same content from other trackers, with better choices about bitrate or codec, or better seeding. I’m not convinced Lemmy has enough users to support a private tracker, I think you need like 20k active users to be worthwhile.
Ideally it would be set up in Lemmy so that a post could remain but the author can be detached from it, and all comments.