i vote also for the limited replacement option, the units in contact with the enemy shoudnt be able to replace all losses, this way you replace your front line unit with another fresh unit or you get weaker.
I think the germans take away his units from combat to reorganize and give rest to them.
The option to have diferent pools of infantry , tanks or planes is very interesting but not resolves the problem of quagmire battlefield. If you have enough replacements you can replace all the losses as now.Perhaps a limited replacement pool of tanks or airplanes per turn...