I don't think something like this would be a good mechanic. It punishes you for hitting the enemy.
It's not a punishment, it's a tradeoff. You have the ability to land a very powerful, unblockable hit (in case of both couched lance and 1h/2h against a horse) but you might lose your weapon in the process. (Making proper sidearms a useful thing for cav)
Well.... cant belieave im reading this shit post from devs.....
So..... more nerfing shit incomming?? srly ??
While you at it, using realism as argument.. make plate immune to cut weapons, implement sprinting, make all wooden weapons breakable, make horses able to kill players when bumping at full speed, make arrow quivers realistic and give them lower ammo ect etc etc ... i could go on an on....
I really hope the devs won't just implement this as cav nerf, but instead use the idea to enhance the way cavalry works in c-rpg now.
As for the realism...
Dropping your lance upon hitting your opponent at high speed is not realistic. Having it break, leaving half of the lance stuck in the opponent's dead corpse would be realistic
I hoped this mechanic could 'open doors' for some actual changes to cavalry (for example making it more powerful, but harder to play)