Plese, lets be analystic.
Cav is OP, everyone knows it, and it MUST BE OP. That's why men started riding horses on combat ... it they weren't OP, they would have left horses for the countrywork. They need a few tweaks, like cavmen getting damage when horse die and they fell 10 meters long, or the excessive, outstanding maneuvrability of the sarranid horses, or getting damage from stomping into a wall (these aren't nerfs, as they have no effect on a "proper" cavman, that doesn't go suiciding into walls or great groups to fall soon) ... but just minor tweaks, the way they work is the way they should.
So what's the problem? The problem is THE NUMBER OF CAV PLAYERS ON A SERVER AT A TIME, when a team have like 25 cavmen at a time, teamwork is useless as you'll be getting raped by horses on every direction, constantly bumped, and pikes are not a fix for that, every veteran player knows it as we've suffered/succeded on each side. Also, the awful autobalance system, that doesn't take into account your "class" when balancing, doesn't help at all.
So, the only thing that's needed to be fixed is that. Just cap the number of cav players allowed to spawn to 10-15% of total players on a team and problem solved (with a horse in their equipment, they could spawn without it) ...
PD: +1 if you like the idea.