Somebody has to own and manage the 'namespace'. If it's not you, it is always going to be someone else.

I think this was one of the motivations for pobox.com. By being primarily a mail forwarding service, you can switch e-mail provider by simply forwarding to another address. The same is true for domains, since most registrars have pretty simple interfaces to set up e-mail forwarding.

The hard parts are dealing with SPF/DKIM (since they don't work well with forwarding) and e-mail migration.