Bluesky is not closed-source, it's mostly open. It's a hard mastodon-circle myth. Aside from being open-source, it's a protocol.
What I'm doing with Bluesky should be easy to reproduce with Mastodon, opening to 10 M accounts more.
People won't create an account to review. Not even a OSM account. We need to build on what's available, and ATProto is spot-on for this usage.