Nice plan!
Could you have one campaign from the part of a German Unteroffizer/a lesser rank if you must, two British Sergeants/lower rank if you must and also maybe a French Resistance guy?
That way, you could have the invasion of Holland (the German guy), Normandy from the British point of view (I'm quite bored of Omaha, to be honest), with a couple of missions being from the point of a crack Glider squad and the results of their missions affecting the final assault on one of the British beaches. That could be good.
And I know very little about Foy, so don't ask me about that
I would say that, whilst one long campaign would be great, the problem with it, as Big Boss Marcus said, would be ironing out all of those little pain-in-the-arse bugs when you have one super-long campaign.