Epic wants you to work on Gears of War 3. They also want to tease the entire human population of the universe by mentioning a "new unannounced IP" in the same want-ad, which could be literally anything.
The possibilities are endless; that's why a secret new IP is always such an exciting thing. Without an existing universe restricting their creativity, Epic's designers are free to follow their whimsy. If we may be so bold as to make a suggestion, Epic, how about a point-and-click rhythm-adventure game set in an alternate future-history, where mathletes compete in life-or-death tournaments to decide the fate of nations? Or, alternatively, a twin-stick puzzle-racer about an army of genetically engineered Marmadukes?