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.
Not really. You can utilise a Mastodon client that allows you to subscribe to remote instances. Another option is to utilise a relay and subscribe to an instance