This is worth checking out from the Bluesky: 

https://atproto.com/blog/feature-skyfeed

Skyfeed is a powerful feed builder with regex capabilities among others. Still easy enough to be used by end users.

This is similar but less so:
http://blueskyfeeds.com/
nostr:note1jwze2cae4zlyfvanfj8ec9agm2rk9ug4z9j9sdydsp76h4pza5qsqxexcu 

 but can those work if Bluesky becomes decentralized? 

 I don’t remember the data structure of ATproto but on the nostr environment the primal type of indexing service could be ideal for firehose type of real-time algo feeds?