sort of sounds like Jetstream for atproto (bluesky) - a way to consume the firehose but you choose which lexicons it looks for (specific apps.)
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this comment makes no sense
this proposal is more client-side, but it made me think of https://github.com/bluesky-social/jetstream which is a way of viewing all of the atproto network wayy more efficiently and you can also filter through it to choose which content you want it to search.