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?
APIs should work, though. So unless the instance needs some kinda captcha or other client-side challenge, e.g. for registration, people could presumably use apps with it.
Plus, if the aim is just to reach and use the instances, and not to be anonymous, then one could probably use a regular browser with a Tor proxy (Firefox can do it per site with both proxy-switching extensions and containers). Assuming that domain resolution would work.
However, in my experience, not many social-media-adjacent apps support setting a custom proxy, even though modern network libraries should make it a no-brainer. E.g. few Matrix clients support that, and ones that do aren’t much of an eye candy (and have problems with the initial setup of the encryption, which seems to be a pervasive issue with Matrix).