The code of the latest Hearthstone has been unpicked by the people at Hearthpwn, and the findings have been quite interesting because they seem to hint at further expansions and what their content could be.
A string of code within the patch points towards what could be a Blackrock Mountain expansion and its presale. There's very little to go on though, so it's unsure if this is a final thing or if Blizzard are still going to make tweaks to have something else happen.
New cardbacks have also been determined from the datamine, although no images have been found. The information is as follows (with 'brm' believed to stand for Blackrock Mountain):
Molten Core
- Reward From: License Detected (Meaning you own the game)
- Note: purchase brm presale
Ragnaros
- Reward From: Ranked Season Play
Golden Celebration
-Reward From: License Detected
-Note: Golden Celebration cardback
The Golden Celebration itself hasn't been determined though. Some are saying that this cardback will be available when you fulfill a certain condition such as winning 500 ranked matches or possibly build a deck of all Golden cards. Others think that the Golden Celebration might actually be something to do with the first anniversary of the game.