I agree that it would be but my wanting to bundle it with SMTP is for forcing the linking of the two concepts -- I guess my argument is less technical and more that I think the two concepts should have been linked early on -- I think if we'd bundled email and instant messaging (aka "live" or "instant" email), we would have encouraged service providers to offer the service in a standards compliant way.

I don't have a preference on exactly how the service discovery would work -- I'm merely suggesting instant messaging could/should have been an extension of the SMTP spec like websockets were an extension of HTTP.

[EDIT] - Looking over the link you sent, that is exactly what would have made a good addition in my mind -- if SMTP had some sort of functionality to suggest that XMPP was available and where to check (DNS SRV records)