There would obviously be a lot to work out, but if something like this was in the SMTP standard (or at least introduced), I think eventually email providers would race to differentiate themselves with support for it, and we might not be where we are today. In my view there's no reason to even require the SMTP servers to serve chat traffic -- as long as they could hand off reasonably, and everything spoke the language as specified in the spec (or at least came close).
