This was actually suggested by the Morgenthau plan, and by the infamous book
Germany Must Perish! Needless to say, both plans were dropped, as the former was unfeasible and the latter was... well, immensely cruel. This sort of action would have resulted in non-ending revolts and insurgencies among the Germans, most likely 20-30 years after the war. The ruling countries would have to rule over a country of German ethnics who would undoubtedly want their own state again someday.