I don't disagree that there's room to move away from email, but how do the current crop of messaging services promise to overcome the problems you mentioned? They all seem as varied in their implementations as you suggest email is.

I'll also add that I think if something were to replace email, hopefully it would incorporate the slow response expectation of it. IM etc usually implies an expectation of an immediate answer; the length and expectation of not receiving an immediate reply afforded by email is immensely valuable.