Your proposed solution isn't really email though. What you are describing has already been solved by instant messaging/jabber/twitter/facebook PM etc. Some of the solutions that already exist need a third part provider, others don't.

The problem to solve is how do you have a fixed address where anyone can contact you, spam doesn't get though and you don't have to maintain personal black/white lists. This is what email currently provides. Granted, the spam part varies depending on the provider.