I've slightly hacked up WordPress to blog in unicode (all that it takes is essentially replacing all instances of 'charset' in files), however, blog by email feature isn't that easy. It simply fails to recognise a message sent to it if it was sent from a charset-aware client that encodes the subject line as per mime specifications if it sees international characters in it - because instead of 'blog:' it's something like '=KOI....blog....', etc when taken literally.
Is there a chance that it will deal with foreign-language messages properly in the future?