By this I sort of mean like, in the case of Lemmy for example, something like a built-in Lemmyverse of sorts.
It wouldn’t be pulling in data yet from other instances, but it would enable seeing that their communities were out there so you could then tell your server you’d like to subscribe/follow/etc. their community/channel/account.
Tbh despite having been around the fediverse for awhile, I’m not sure how else ActivityPub servers were supposed to have these different things found to start with.
It would have to pull some data, but it could be much less than federating every community.
I think it would be great if, as soon as two servers become aware of each others existence, they automatically federate each others lists of communities, and possibly the sidebar info.
Federating the rest of the data would happen only if someone subscribes to a community from another instance, same as it is now.