You don't need a single autonomous domain, you just need a web of trust where other hosts are allowed to send trackbacks/webmentions to your site once they prov

You don't need a single autonomous domain, you just need a web of trust where other hosts are allowed to send trackbacks/webmentions to your site once they prove free from abuse. That's essentially how the Fediverse works - bad servers can simply be banned from the network. (And the Fediverse shares a lot more than simple backlinks, so the risk of abuse is correspondingly higher.)