Follow up, 2025-12-27: Rudy here confirms the Blacksky appview is still being worked on (eg: blacksky uses bluesky's appview still)
https://bsky.app/profile/rude1.blacksky.team/post/3maykethsbk24
The sticking point, as he describes it, is "backfill". This alludes to the issue that makes me compare ATProto to blockchain: to get the features users expect, every node on the network must mirror the network's entire history. This is impractical, which is why bluesky is as of this moment a federated network with effectively only one node.