Will never happen, why, because there were no americans in the middle ages so cannot be made overly patriotic, like every single Cod game has been...
Also cod is a shooter, your limited to bows, and crossbows, and throwing metal things, and possibly flaming arrows in middle ages, and how do you upgrade a bow and arrow,
no, just no...
Could work but definatly not on the cod engine, would need to be built from the ground up by people like oblivion makers with a hyper realistic engine which could compensate for armour density, bleeding, horse riding, sharpness, speed of swing of sword and enemy ai when swords and arrows are involved, maybe a possible hardcore game for the new motion sensors, i could see it on the move, the cod engine just couldnt make this work expecially looking at its present meelee capabilities...