Hearthstone: Heroes of Warcraft will receive around 100 new cards when it is next updated. Production director Jason Chayes confirmed this in a recent interview with Polygon:"We are going to have a central theme for how that will all fit together. That'll be the next thing coming up," the dev explained.
For the incoming DLC Blizzard took a closer look at the pacing of Hearthstone, and "not just the pacing of the game as it is, but pacing of the rollout of new content." The new content should be good for seasoned players as well as newbies. No word on when the next update will go live, but Chayes promised some news soonish.