I think there is a lot to be said about improving e-mail but that being said many of the decentralized privacy benefits are lost when you rely upon a 3rd party hosting. On the other hand hosting your own email server is a pain and so is dealing with spam. I'd be interested in a project that made it easier for people to host their own e-mail and/or made it easier for people to port their accounts. I know some work has been done by the LEAP project but also people have migrated towards app based encryption/security because email isn't very secure from surveillance.