Hit whoring ahoy!
The latest issue of Entertainment Weekly has a big Star Trek cover story (see Evan's write-up here). It has two cover stories, really - one has Kirk and Spock and the other has Kirk and... well, John Harrison, but the official EW description of that cover is "Kirk & Khan."
The premise here is that whoever does data entry on the EW website had the inside knowledge that Cumberbatch is Khan. While the text describing the article indicates that Abrams remained shtum on the matter, some aspect of the process between getting the photo from Paramount and getting it on the website revealed the character to EW. I mean, it's possible. I've seen stuff leak out through mishandled publicity materials. More likely this is a function of SEO tinkering or somebody just thinking "Kirk & Harrison" made a shitty headline.
I do still think that Cumberbatch is, in some way, Khan. I just don't know that this is the proof.