United in Stormwind Cards List & Guide
Ok so usually the cards that change are the 5 cards you can cycle through in the following page:
http://us.battle.net/hearthstone/en/ (usually those are Illidan Stormrage, Fireball, Gadgetzan Auctioneer, Grimscale Oracle and finally Bloodlust). If they were giving clues despite the leak then I presume that they would use cards that exist in the game such as King Krush, which are also related to the location of the expansion thematically.
Now onto the card I was right it is called Darkspear Hunter and you can see it on:
If you really want to check for the art that was previously shown there you can use
which will allow you to see the versions of the hearthstone page previously available to see if the card art has indeed been added, but I really doubt it since I remember seeing it there before.
Yeah it has been there before. It used to be a Hunter minion (I think), but was then removed from the game and not used. Could be that they use the art again with the upcoming expansion, but it is old art for sure and it has been on the page before.