Time for another suggestion that's too late and too much work to be implemented
I have always wondered why spells are not targetable. After all, regular missile troops can pick whether to fire at commanders, mages, archers, etc., so why not troops that hurl magical attacks toward the opponent?
Say I'm Ulm, fighting against a feudal independant - If I could have my smith aim his 'blade wind' at the longbowmen, rather than at the knights who it won't trouble in the least
it would be sweet
Here's why it wouldn't work though: suddenly certain spells would become really overpowered - like for example 'mind burn', and any other high precision damage dealer.
If there were a way to make it work without screwing the balance entirely I think it would add an element of strategy currently lacking. And it would be sweet