Apple has begun sending out emails to inform iCloud users that @icloud.com email addresses have been reserved for them. These seem to be directed towards previous MobileMe users who had @me.com (or legacy @mac.com) addresses. I don't recall email addresses being reserved following the mac.com to me.com transition, and icloud.com, and there's no additional information or context provided. The email simply states:
All new iCloud Mail accounts now come with an @icloud.com email address. As an existing user, we'd like to offer you this new address as well. We have reserved [redacted] for you, and you can now use this address with your iOS devices and computers by following these simple instructions.
If you prefer, you can continue to use your current email address just as you always have.
No matter which address you use, you'll continue to receive all your mail, whether it's sent to your @me.com, @mac.com, or @icloud.com address.
Whether this has something to do with previous, additional MobileMe aliases or something else, I'm not sure. If you received an iCloud email reservation from Apple, let me know.