A couple of points: 1. War weariness still stands. 2. Levying units still costs gold and have limited time. They not necessary pay off. 3. Even without warmongering penalties, civilizations you have war with will not like you, you'll be unable to trade with them and you'll lose envoys with city-states you're at war with. But the idea to have war on the other side of the globe with levied units to pillage - it sounds interesting.