You’ll have to go complain directly to the W3C for that. The situation is Lemmy may fix it with some custom protocol extensions, but then it’ll still break every other piece of software that follows the spec like Mastodon, Kbin and others.
It’s like adding a 6xx status to HTTP. You technically can, but expect every standard compliant clients to be confused and bail on it.
You can’t just change domains with emails either and have everything seemlessly migrate over. Not losing a domain is not a completely unreasonable assumption to make.
Thankfully the users and communities aren’t lost, it’s just that people outside of fmhy will have to resubscribe to the communities on the new domain.