In retrospect, we dodged a bullet because, for mailbox local
parts, ARNE does not, in terms of anything a sender is allowed
to predict, match arne. That BLÅBÆR doesn't match blåbær
may still be a surprise to some, but it is not more or a
surprise.
But MTAs can and do treat local parts any way they want. Do EAI MTAs
do this sort of langauge-sensitive mapping on incoming non-ASCII
addresses? There's no reason they can't, and the advantages of doing
so are obvious.
I can see problems where systems are large enough to be used by
recipients that speak multiple languages, but I'd think that it can
usually guess what language a mailbox is in, or it can just ask when
the address is created.
R's,
John