I know everyone has wanted a completed TATW mod since medieval 2 kingdoms but to be honest there wouldn't have been much of a change in terms of troops, siege engines, cities and landscapes if it were created on rome 2 / attila. BUT NOW, seeing "The battle of Black Fire Pass" on youtube and the kind of units and landscapes which have never been seen before in any previous total war I think a TATW mod for this would result in the closest representation of middle earth ever created in total war.
Imagine seeing the Witch-King of Angmar and his Nazgul followers on Fellbeasts actually flying along with Gandalf using spells whilst he fights them off.