I actually don't know how to interface it at all with steem. If I did I'd probably already be working on it.
And no... not Hearthstone or Magic like other than the idea of the cards. Though making something like those might also be doable if the right functionality is there...
If that is the route someone wanted to go then something like this asset could speed that up a lot:
https://www.assetstore.unity3d.com/en/#!/content/52739
Mine would actually be more of a 3rd person wizard dual on a decent sized level where the units, structures, and spells you could bring to bear would be tied to the card deck you build. :) How you draw cards, and such would be part of the level itself.
If these basic hurdles can be passed it'd open up the doors potentially for a lot of games. I am talking about games that do not live on web pages, but that still tie into the steem blockchain.
Web page based games would also be possible, but they've expressed concerns over security problems that could occur due to embedded web game code.