For one thing, it would break mail to the majority of mail users who use ASCII mail clients.
Would it break them any worse than keeping the addresses in Unicode?
Uh, what? EAI mail is defined by RFCs 6530 through 6533. One of the things they make crystal clear is that the EAI mailstream, with Unicode addreses, is separate from the ASCII mailstream. We tried for a decade to come up with clever ways to downgrade addresses on the fly, all of which failed miserably in practice. It appears that you are suggesting we abandon the IETF standard EAI mail and invent something different. No. Or if you aren't, then I don't understand what you are suggesting. Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly