Sometimes implementing a new IETF extension RFC that makes sense, but quite often not, because being among the first to implement rarely makes sense. Unicode mail is like that: Why bother to implement unicode addresses if you can't send mail to anyone and noone can send mail to you?
Well, gmail has done it and in hindsight, of course it makes sense. Half the world's email is on gmail, so their first customer to use it can already exchange mail with half the world. Google has to sell Google Apps for Business to some Chinese and Japanese companies who currently use Exchange, then the investment is paid for.
Update: Those first customers don't even have to use unicode addresses. Being the first to use a unicode address is perhaps not much fun, but being able to receive mail from that first user is 99% benefit.