Actually, including 1948-1991 once EvW: A Hearts of Iron game is finished.You ask that but they've updated CK once, EU three times, Victoria once, and HoI twice. Of course, it honestly wouldn't surprise me if "Fall of Rome", covering 476 to 867, was made. Couple that with a Decline game for 27-476, and we'd basically have playable history from the Pyrrhic War to the start of the Cold War.
But, the one most likely to be updated next is HoI, since it's the oldest.