Or volunteers. Don’t know about where you are, but near me, town gardens, flowers, woods and rivers are maintained for all by community-minded volunteer groups.

Sure, but there’s a distinction between maintenance and profit.

If that requires a maximum ratio of active users to average donation, then it’s feasible, and has the potential to survive with a more invested userbase than a site that’s severely bloated with lurkers.

I personally think the model of the old style ISP actually made a lot of sense here, but I'm guessing it might never come back. Back in thr 90s, you paid your ISP for Internet service. But that was more inclusive than just a data pipe. You also got space for a small personal website, text usenet, and email.

This made a lot of sense and back then the services didn't need to have ads or tracking, you paid monthly for the bundle of services.

I don't know if federation will actually take off, but I can imagine needing some sort of paid hosting for large groups of people on large style services. Maybe that will be some ISPs, but more likely it'll be either "federated services" companies that for a monthly fee run a bunch of the popular fediverse tools like Lemmy, Mastodon, Matrix, Pixelfed, and maybe Peertube. Possibly through in email too idk. Or you'll end up needing a per tool subscription to a company. Maybe donations will work, that'll really depend on how this scales.