I've always toyed with ideas of how to make games have a real "fog of war" effect. I think your use of cards does well in keeping things clear but still allowing for all orders to be given at once without getting to confusing or cumbersome.
The rules as written do skirt the line of making this an almost different game, rather than just a different mission in the existing OPR game. I'd have to try it out once to really get a feel for it. Have you been able to play test? How did it work?
There are shifting objectives, but only to the extent of which objectives to capture. It still feels like a standard game of grabbing objectives.