FDR’s Treasury Secretary, Robert Morgenthau, proposed something not quite as radical. It was to completely de-industrialize Germany and leave it an agrarian state. The resulting population losses (~60%) would be incidental to the overall goal of ensuring that the country would not present a threat to its neighbors for a long time into the future.
Your proposal is along the lines of Timur’s “mountains of skulls” approach to conquest.
It has long been speculated that the author of the “Morgenthau Plan” for the `pastoralization of Germany’ was a communist, one of many in FDR’s administration, and who deliberately leaked this `plan’ to the Nazis to provoke them to fight hard against the Western allies, allowing the Red Army to conquer more of Eastern Europe & Germany.
Otherwise, the theory goes, the Nazis might have made an advantageous truce with the Western powers which would have freed up all their forces on the western front to go and fight the invading Soviets.
My Dad was in Patton’s Third Army & this was the general view of the Morgenthau Plan among the troops.