I'm still to play with a proper cavalry heavy faction BUTT:
-Mounts that lose their rider can still influence combat. Some are literally more powerful than the rider (Bandar's tigers, Nigger spiders)
-A surviving mount makes rehiring a rider in the same province cheaper. Because you already have the mount. Exact mechanics of this currently unclear.
-Dimsounted riders keep fighting, you need to kill the knight after the horse, usually.
-Dismounted riders that survive combat can retreat and find new mounts automatically.
-Cavalry that retreats from combat with both rider and mount is almost guaranteed to make it back to a friendly province, this opens up possibilities. Maybe. Still need to test stuff.
-Spells can affect mounts and riders differently. Charm the rider and the beast remains, dominate the animal and you still have the (now pissed off) rider.
This simply from the top of my head. I'm pretty sure there's much more. Also diz:
This thing count has riding 4 mounts. Memetic potential over 9K. How kewl is that?