FWIW, I recently had an idea for a federated network that might actually work, because it's actually limited in knowledge and computation needed at each node. I'm currently calling the idea "The Dungeon", but I may switch to "Dante" if I feel like it, because it's sort of structured like descending into an upside-down, pyramid-shaped Dante's Inferno.
The idea: there is no separate client. You install the client/server, which has no additional dependencies, and it becomes a small pyramid-shaped chatserver with 1 + 4 + 16 rooms and a hard cap of 16 people per room, maybe less if you want to use fewer resources. Each room has 5 exits: four "down" for each cardinal direction, plus one "up". You can link the "up" of your top room to a "down" of someone else's server, but only with their permission (achieved outside of the network). Your server knows and persists shared secrets for all servers it has ever been connected directly to, and each room has three slots for persistent messages ("scrawling notes on the walls to your fellow damned souls"), with each new note beyond 3 overwriting the oldest, and you can ban people from entering your server based on the path from their home server to yours.
(Note that a path is actually just a string of bits, since each level has exactly four "down" links i.e. two bits of data. You don't really need to know which rooms are on which servers when banning, since your path is relative to the top room of your server.)
Beyond those three pieces of information, absolutely nothing is persisted, so the storage requirements are simple and backups are mostly unnecessary except for well-connected instances higher in the pyramid.
If the per-room or per-server limits are exceeded, it triggers an "eruption". Basically, people in the affected server get flung out the server's exits more-or-less at random, with the probability of an eruption going up faster as more people are present, frequently triggering chain reactions if that part of the network was too packed. Rooms toward the bottom of the pyramid would, I imagine, naturally tend toward in-depth conversations on heavy topics with people who know what they're talking about, while rooms higher in the pyramid would naturally tend toward arguments and, perhaps, actual healthy exchanges of ideas. But with a max audience of you, the person you're shouting at, and 14 other people.
TL;DR: kind of a federated MUD/MUSH/MOO thingy, but built on the idea that "hierarchies of communication are good, hierarchies of status are not good, and hierarchies need to have consent via boundaries and banning".
OTOH, this idea came to me while I was outrageously stoned, so maybe it's useless.