Given the US recently made a bid to fast-track multiple censorship bills, KOSA included, and is also trying to kill Section 230 now, which will pose an existential threat to Fediverse instances hosted over the clearnet, how feasible would it be to host said instances over Tor/I2P?


Not feasible.
Just use an instance that is outside USA and not using a USA hosting company? Half the fediverse uses Hetzner, for example. OVH (French) is another popular provider.
I’d probably choose somewhere outside of France. Hetzner probably a better bet.
Of course it’s feasible. Easy? Maybe not.
Good recommendations though.
I took the question to be “could you currently host fedi servers on the dark web, without any big changes to their code” but yeah I’m sure it’s possible to make it happen, if people wanted to put in the work.