I call this idea the "feed marketplace" as opposed to "feed-as-a-service" which is what @openrank and others are doing. 

The challenge building a "choose your algorithm" is that the most interesting feeds are no longer just "algorithms" or fancy SQL queries.

imp nuances in @v's thread
-feed marketplaces add burden on users, require many levels of abstractions
-feeds can't sustain with stale SQL queries,they need model tuning+low latency infra
-ranking users/casts is fundamental for good feed 
making rankings configurable for clients is a big unlock vs algo choice for users

Technowatermelon. Elder Millenial. Building Farcaster. 

nf.td/varun