Always wanted Cav to be more dynamic in Warband, but playing for years as Cav & Inf, i got used the mechanics of cavalry, (and i think many players fell same and dont want big changes in my opinion) drastically changing its gameplay and making it more realistic won't fit M&B at all, one of the simple reasons is that, people won't like realistic horses, I'm always up for realism in games, but horse collision must not become death sentece to the Rider.
Vikingr has interesting Cavalry mechanics, time to time, running over your enemies in battle will cause you to fall off from yer horse, also in The Deluge mod, when enemy shoots you or hits you with melee weapon and survive, you fall off from horse, which is really good for gameplay, but making it so that your horse thinks by its own durning the battle is interesting yes, but will be hype killing for many players.