That's interesting. Do you know where the requirements are published? I've read language recently from at least one registrar specifically stating that private registration prevents transfers to other registrars. Maybe this was before these new requirements were published.

In my recent experience, private registration prevents transfers because you are unable to receive the email message that contains the code you need to complete the transfer. I am still able to transfer my domains, but I need to turn off private registration first, so the email is sent to my real email address. This seems like a silly problem, and one that the registrars cold solve if they wanted to, but obviously they don't.

I have transferred multiple domains with the privacy service turned on. No problem whatsoever. Every registrar worth doing business with (i.e. not GoDaddy) will forward all important mail to your real email address. Emails can take a few minutes or hours to get forwarded and/or end up in the spam folder, but that's about it.

If your registrar's privacy service is so bad that emails don't get through, transfers should be the least of your worries. Because of the new ICANN verification rules, you're at risk of losing your domain if emails don't get through to you.

I believe some of the registrars provide a rolling email address on your whois info, which forwards the mails to your inbox. But the address is changing at intervals, therefore if anybody scraped the address it won't be of use.