it is highly unlikely that IDNs will change the email syntax.
OTOH, any attempt to bring Internationalization into the local-part will
almost certainly onvolve some restriction on its present flexibility, as I
showed when we discussed this a few weeks back. That needs to be looked
into before we cast it into concrete in its present form.
I don't see why introducing I18N into the local-part need restrict the
syntax or flexibliity for non-I18Ned local-parts. As long as the I18N'ed
local-parts are a subset of the current syntax then I don't see why this
needs to affect 2822 or its successor.