Starting with BlizzCon on November 1st we will know more about the upcoming Hearthstone expansion, but there have already been some leaks.
Today, Daniel Ahmed, Senior Analyst at Niko Partners posted on Twitter that the newest Expansion will be focused on Dragons. Galakrond will be a special hero card for the evil classes. I would say the person is trustworthy, so the leak should be too.
The Evil Classes are: