We had that in coh1.
It prevented you from reinforcing infantry if you had mechanized gameplay, pretty much PE problem, which is DAK here.
Well what's the problem with that? In CoH2, for example, we have soviets choosing between T1 and T2, either opting for stronger infantry or better teamweapon support. You're giving up one for another, (or you could do both at great detriment to yourself) just like you theoretically might be doing in this situation for DAK; you either play mostly with infantry, mix both and play around manpower starvation, or focus mostly on vehicles.
I don't personally see that as a big issue, especially when DAK has all the tools necessary to make infantry gameplay work, as well as having powerful vehicles to base their mechanized gameplay around.
It would also temper the base battlegroups a bit, especially the tiger, which only has that manpower cost. If you've been pressing the advantage with tanks already, and paying manpower to keep them in fighting shape, then I think it makes perfect sense that you shouldn't be able to easily snowball with the 900 manpower Tiger. (Which would otherwise be easy because Tanks help to minimize manpower bleed without such a mechanic.)
I also didn't play CoH 1 PE extensively (or any faction particularly much), so maybe there's some huge element to this that I'm missing here.
Tying it to only the heavier vehicles would alleviate the PE/DAK problem, in any case. Your Ultralights and Lights don't bleed, but perhaps your Tiger does.
I'm sure there's space to play around with this concept again.
I agree. I don't think it's a bad idea in principle. Unless Katitof can bring some examples as to why it crippled PE in CoH 1 or something.