If they do that, then they should make the horse a player character, because you'd a second guy to steer. A good trained warhorse knows how to smash through people and not smash through walls.
Plus I love seeing the panic in a cav's eyes when he hits a low wall or rock he didn't see, and all the archers and throwers are lining up on him. And I love it even more when the cav gets swarmed by a group of infantry- first the horse, then the rider. You can't see what's happening to the rider once he goes down, but I imagine all the infantry are totally destroying the corpse and ripping it to shreds.