The subject was heavily debated during the development of the 2nd edition core rules and eventually it was decided it against it.Taking it further, there is actually one other big change I would make, and I've written this loads of times before but hell I'll write it again. Split leadership into Courage and Discipline. This would make things sooooo much simpler and making giving each army it's character so much easier.
Discpline covers marching, formations (bring back columns! shieldwalls, testudos, open formation (adopt skirmish basically)), basically getting your units to do what you want them to.
Courage covers how brave they are in a fight, so break tests, terror etc.
You could get rid of soooo many special rules with this, and really give races character and flavour. So e.g. a savage orc would have appalling discipline, but better courage than a normal orc, you don't need any special frenzy type rules. A dwarf hammerer would be outstanding in both. It solves this issue of how do you make elves and dwarves feel elite without having to have ridiculous fighting stats compared to a say an orc bigun. It would also make the game more about manoeuvring and generalship than just list building and spell combos. More a wargame, less a high fantasy warband game.
EDIT: it's far from a new mechanic, this existed in 3rd edition and was much loved, hell GW even started selling the 3rd ed book at Warhammer world because people still want it.
I would need to go and dig through the relevant topics buried somewhere in the archives but if I do not recall falsely the split was not chosen as not to further increase the complexity of the statline as well as the game for little in game difference since overwhelming majority of units would have the same value in both categories or just a minor 1 point difference without making them unplayable in certain aspects of the game.