Yes, I would like the player to be unable to use weaves whilst on horseback, what with you being able to just circle the enemy and sling fireballs at them. I also believe that it would be a good way to promote use of other weaves. As it stands I generally use shield, seeker, fire curtain and fireball and I can destroy quite a large amount of channelers as well as normal troops. And I can't recall any battle weaves being used from horseback, they would require too much concentration to use (I think) what with Rand having to stand still whilst channeling to his maximum. So at least make it cost more to use on horseback?
And I also believe no non-named should be able to channel from horseback at all. They the "Rank and file" channelers so yeah...