That would make a really good addiction to Oblivion.
I mean a mod were you could damage enemy with the horse's strike, and it would gain strike level... So they could even attack other horse, like medieval duels.
Mounted combat just seems to iffy, this and multiplayer is just the stuff that people want that Bethesda can't deliver without extremely delaying the game and creating wierd glitches. I for one am glad they are not adding mounted combat actually.