I'm not going to go out of my way to accept these domains.
If Exchange / postfix / etc. don't support them in their latest stable version, and a couple of stable versions before that, I'll likely never see them in use anyway.
The way to deploy something like this is to be low-impact (punycode stuff isn't), backwards-compatible, and get the software working first before you start selling such domain names en-masse.
Chances are, most people who buy those domains will quickly discover that nothing works for them and nobody ever answers them, then stop using them. By the time the software does catch up, nobody will trust them (or their "fixed" replacements) anyway.
Honestly, I see no reason that punycoding something should affect existing email rules anyway. If it's just as simple as allowing hyphens in the domain name, that's a one-liner of a patch to the majority of email software out there and nothing else should really be affected. But unfortunately, it's just not that simple.
And, I've told you before, Reg. You can mention IPv6 when you put out an AAAA record for your own domain. Or did you not bother to write that into the spec for whoever did the new design / CMS for you?