Hearthpwn recently translated an interview with Hearthstone Executive Producer Hamilton Chu originally published on Chinese website nga.178.com. Hearthstone's future is being discussed with the addition of new premium content.
Game content and features
They're working on new heroes like Varian instead of Garrosh for warrior decks. New card backs are also being considered and these are separate from the ones that are to be awarded during ranked season play (with even more rewards to be planned for the ranked ladder season). New game boards are also going to be added. There is no plan to adjust the length of seasons yet although the team is watching it carefully.
For the time being, Hearthstone will consist strictly of Warcraft themed elements. Anything not Warcraft related won't be added. The game will eventually feature achievements. Adventure modes will have new quests, new game stages, and add an additional 10 to 20 new cards. Expected release date will be some time after the game is official released on the PC and iPad.
Even though Hearthstone isn't out yet, the developers are looking ahead and planning the first expansion which will likely contain 100 to 200 new cards. Chu confirmed that Death Knights and Monk classes are not being worked on. 2v2 mode and observer modes are not actively being worked on (although observer mode is on the to-do list).
The fact that an expansion is already being planned is a good sign. Looks like Hearthstone is going to be here to stay for sure. Good on the development team to focus on the core aspects of the game before expanding and adding other features. I played two-headed giant in Magic: the Gathering but now isn't the time to add it. I'm a little sad about observer mode but delighted to know that there is a plan for it.
Let's talk about seasons for a moment. Hearthstone seasons are around a month long. I've chimed in on this before, but one month is just too short. Starcraft 2's World Champion Series runs about two to three months. However, most Hearthstone matches don't stretch out that long. The longer a ladder season is around for, the more stars there are in circulation (largely due to win streaks as you earn an extra star) and it allows more opportunity for players to gradually rank up more.
If you haven't yet tried the game out yet, the open beta has started in North Amerca (and for Europe). Test Season 2 is ending at 11:59 PM Pacific on January 31st which means everyone's rank will reset to 25 and Test Season 3 will start.