Has any thought been given to how such charsets will appear in mail
addresses?
yes, folks in the IDN group have talked about it. since there's
already a need to encode characters that appear on the right hand
side of an @ sign in ASCII (because there are so many applications
that assume that domain names are ASCII), it might be that the same
encoding convention (or a similar one) will work on the left hand
side of an @ signs.
this would have the advantage of not breaking existing UAs and
MTAs that expect addresses to be ASCII.
Keith