[account42]

Seems the real issue is that Mastodon is too hard to self host if not even Wikimedia wants to do it.

> it'd involve giving a third party a SSL certificate for wikimedia.org

You can have certificates for subdomains. With Let's Encrypt you still need to control the root domain to generate them so they'd have to setup something for that. But that's more a can't-be-bothered concern than an actual security concern. Teaching the public to trust random domains being authentic is a much much bigger security concern anyway.