Google tried this with Wave and they failed. I wish they had succeeded. I think they should have spun it was "Email 2.0" and made the transition easier.
I think we'll see it again, though not necessarily from Google. What failed about Wave was the way the project was organized and pitched to users, not the idea.
Personally, I don't see what Wave has to do with email, it's a completely new protocol that wasn't integrated with email in any way and that's why it failed. They should have done this from the start: http://code.google.com/p/wave-email/wiki/Outline
Google wave was also horribly complex. Email needs to be simplified, not just added to, which Google keeps doing with Circles and other stuff that they keep bolting on to Gmail. Reminds me of how MS used to do stuff.
I actually loved wave, I think they would of succeeded had it been tied in to your email account. I had to remind people to send me messages @wave.google.com or whatever it is. If all my gmail messages automatically went to wave and vice versa, I think it would of succeeded.
Google tried this with Wave and they failed. I wish they had succeeded. I think they should have spun it was "Email 2.0" and made the transition easier.