I thought about this a while ago. My conclusion was that the simplest way to handle this would be to copy multireddits, and expand upon them.
Here’s how I see it working.
Users can create multireddits multicommunities multis as they want. What goes within a multi is up to the user; for example if you want to create a “myfavs” multi with !potatoism, !illegallysmolcats and !anime_art, you do you.
The multi owner can:
edit it - change name, add/remove comms to/from the multi
make the multi public or private
use the multi as their feed, instead of Subscribed/Local/All
use the multi to bulk subscribe, unsub, or block comms
By default a multi would be private, and available only for the user creating it. However, you can make it public if you want; this would create a link for that multi, available for everyone checking your profile. (Or you could share it directly.)
You can use someone else’s public multi as your feed or to bulk subscribe/unsub/block comms. You can also “fork” = copy it; that would create an identical multi associated with your profile, that then you can edit.