The only real problem with the Replishment System we have now is that there is absolutely no way to cut an army's 'supply' of reinforcements unless they are somehow locked in enemy teritory -- which doesn't really ever happen.
The thing is, supply chains have been hugely important since the dawn of warfare. Yet there is zero representation of this. I'm not sure exactly how CA would configure zones of supply into their current engine, but I certainly hope there is some form of Supply in Rome 2.