See https://www.pfrazee.com/leaflets/3lzhui2zbxk2b for some recent thoughts from a team member.
Bsky is likely to put out a short-term gap filler this year for personal-private data, which kind of already exists today for Bsky only. This work would make that same feature in the per-user repo available to all apps. Right now it's hard coded to a specific NSID and single db row