unique IDs can’t be a thing on a federated system.
Twitter does this service, it costs money, and you trust them. the matter of trust here is what you need to separate from the service. if a company like IBM or a financial institute had their own Mastodon instance not open to the public but just to their own verified users, you would not have a problem believing @email@example.com was the real deal, because that server is not open to registrations. there will be other such services popping in the future, and you will be able to find authentic celebrities on such servers. probably not on mastodon.social itself.