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.
