I agree. The real solution is hardened authentication getting baked right into email. I'm all for UTF8 domain names and email user names, however if the email protocol suite is going to be expanded to allow for more features, then I think security should be top of that list.
Sure, for a while, domains that span multiple character sets such as hotmail.com with a Cyrillic o could be spam flagged, however what happens when (not, if, but when) legitimate domains with multiple character sets start appearing? What about domains that use characters restricted to the intersection of two character sets such that they appear to be from one but are in fact from another?
The ONLY answer to this is an email client that can associate a certificate with a domain and checks it against received email as a matter of course. This solution not only has the property of preventing domain spoofing, but also comprehensively solves the spam problem. (It didn't get done earlier because it fell foul of the "requires everyone to agree at the same time" point on that pro forma "Why your proposal won't work" sheet.)