Okay, yeah, doesn't seem to be too many out there. So no real way to do this now, except what you described. You can follow specific people, but no local timelines of instances.
Yeah, there are also interesting experiments out there, like some instances run bots to try to "collect them all" and follow almost everyone they can in the fediverse. The one that found my instance first was @federationbot@mastodon.host.
It's not something I've considered on my instance, to keep costs down and because I like the opportunity to curate it manually a bit.
