Through all the haggling and hair-pulling in the past months over more austerity, fewer creditors getting their money, and a dreaded “Grexit”—a scenario in which Greece would leave Europe’s currency union—at least four prominent economists in three major American publications have casually and quietly suggested there may be a third way: A German exit. That is, Germany should exit the euro, and clear the way for countries in the south of Europe—notably, Greece, Italy, Spain, and probably Portugal—to reconcile their debt with a greatly depreciated currency and maybe finally get a handle on their economies. The latest thinker to suggest...