On the Fireside Fedi interview with Jerry ( the admin of Infosec.Exchange Mastodon instance ) a scary truth was suddenly revealed ( on 34:11 ): Just to keep the instance up and running he needs to spend up to $5000 a month, pretty much out of his pocket. Donations to the instance barely cover any of that. And if he will ask people to pay to use it, they will, rightfully so, switch to a different instance.
Personally I think self-hosting (Docker containers and stuff) would be a good solution, but for the Fediverse that would mean making a ‘family size’ edition of the server software.
I imagine if it became a common hobby and every geek interested supported ~4-25 friends, it might work.