I think it would be cool to be able to switch relay group to, say, a set of relays focused on a hobby, (kind of like an old forum) it could be like discovering a new, hidden country.

I want lists for pretty much the same purpose, but maybe a little more focused on specific people.

You log into the relays, read a curated feed of top posts there, and start saving the npubs you are interrested in into lists.