Product

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.

For most users, what they say they want in a feed and what they actually do is a textbook example of stated vs. revealed preference.

I also don’t see how anyone can realistically monetize feeds for a feed marketplace 

Most users will just use the default

Consumers won’t pay for a custom feed 

Clients will build their own vs pay for alt options that very few people use

Right. It’s a client thing. Multiple feeds is a feature of a client. Infra is expensive!