I've been thinking for some time about a mechanism that could be used to assert control over a domain that has a lot of third-party backlinks to it, as in widgets, ad networks, javascript etc.

Because when those domains become defunct or expire, anybody recognizing what they were could grab them and inject malicious code into all the websites with the broken widgets embedded (we've seen this happen with crypto miners, etc)

This kind of a mechanism (along with domainconnect) could work - but it would also need the browsers (perhaps with a plugin?) to verify a domain on embedded components before rendering them.

That would add a lot of DNS lookups though.

Overall a good effort. Would be good to see something along these lines gather some traction.