I'm just about finished with the fifth book, the most recent one. There's plenty of material to do a pinball machine. Heck, it's going to be based on the show anyway and they have, not quite, caught up to the books.

Honestly, that's the biggest problem. Unless this season is really slow it's probably going to catch up to the end of book five. Supposedly, Martin has told the HBO writers how the series ends, but, that's no fun. For a TV show's narrative to travel beyond the book, its source material.