After digging in the release notes, we found that Apple is starting to use @iCloud.com email addresses for any new user signing up for an iCloud mail account. Current devs with a @me.com address will automatically get an @iCloud.com one.
●iCloud.com email addresses are now available for iCloud mail users. Users signing up for new Apple IDs, or enabling Mail on their iCloud account for the first time, will automatically receive an @icloud.com email address instead of a me.com email address. iCloud users with @me.com addresses that have been used with iOS 6 beta 3 will receive an @icloud.com email address that matches their @me.com address.