So, one of the card backs that was revealed quite some time ago has finally been revealed! It's the one 4th one along, with the blue center and yellow tavern window effect. Click on the image to get a better look at it.
http://www.hearthpwn.com/news/448-in...get-a-new-card There's a news post on Hearthpwn explaining how to obtain it, though it's disapointing to see that the events are all US only for the time being. Another slight downside is the need to gather 3 people as I could quite easily do it with the two PCs I own, yet I'm one missing, so I might borrow a friends iPad and get that bonus pack too!
That's now 4 out of the 6 backs with ways to obtain them. Using the above image, the first is the default one. Hitting legendary rank gives you the 3rd, this new event gives you the 4th and placing in at rank 20 or above for season 1 gives you the 5th. That just leaves the 2nd and the 6th up for speculation. I'd sugest that the 6th is to do with the new Naxramas set that's going to be released and that the 2nd is either for hitting rank 20 in season 2 or another event.