I would love to see S.T.A.L.K.E.R. with the game mechanics and open-world-ness of DayZ, only, like 1000 times better, and with an actual, like, 5000 square kilometer area, just like the actual Chernobyl exclusion zone.  Some RPG elements, a system to prevent completely random KOS, possibly a singleplayer with a really badass storyline, and a multiplayer which is basically just an RP sandbox.  Holy shit, that would be the best thing to ever happen to me, I would never log off.