More at the source
Yesterday on Reddit, a poster named UndercoverLegend wrote that he snuck into Digital Extremes’ office, took lunch, and started talking to other employees there, who revealed that the studio is working on a card game called Keystone.
Reddit’s mods have since deleted the story—which I’ve independently confirmed is true—but we’ve got it here:
Keystone is "a FPS with cards (like magic the gathering style perhaps)"
Source (Kotaku)