Not really. I mean, sure it’s the same concept, but email has been getting semi-centralized between the big players now, with gmail and maybe icloud getting the largest chunk of users. That would be similar to letting users choose between .world or .ml to sign up with, which is against the fediverse principle to spread the load as wide as possible.

When you present the lowest common denominator internet user with hundreds of instances to choose from and requiring them to think further than clicking through a sign-up page, you lose user interest pretty quickly.