I think that's a really cool idea, but I am apprehensive about unforseen consequences. I have previously pointed out that the current structure of Lemmy creates a nice balance of power between admins, mods, and users. I think all three groups have enough agency and independence that they can follow their personal preference in the fediverse without infringing too much on the experiences of the others. In theory, as the network expands, stability will continue to increase.
I'm not sure about messing with that paradigm in order to implement something like what you're describing.
The question is: who else would be interested in hosting these fediverser-enabled instances?
So just to clarify what you mean. The fediverser-enabled instances would be current instances like lemmy.world, except with additional functionality to subscribe to unaffiliated communities?
Or they would be a totally new kind of instance with only independent communities? Sort of like lemmy.myserv.one (they don't host local content), except instead of subscribing to communities on other instances, you would be subscribing to standalone communities organized in some kind of lightly moderated community list.