I made a test and, interestingly, I /can/ send an email to myself setting up the header like this:

h.append(b'My Name',         charset='utf-8')
h.append(b' < ',             charset='us-ascii')
h.append(b'my',              charset='utf-8')
h.append(b'@email.address>', charset='us-ascii')

The message in my Inbox will then have a To: header along the lines of
"=?utf-8?q?My Name?= <=?utf-8?q?my?=@email.address>
so the mailers are sure nice to me.

The startling part of it all seems to be that such email addresses are already out there and seem to be supported by enough mailers, albeit not by enough client-side systems.

With this non-standard approach and RFC 5335, I feel tempted to hope for a helper method which finds "the" ("an") canonical form of an email address...