I thought it might be nice to give faction mounts more of a practical use, rather than just cosmetic. They could give a stability bonus against dismounting either in the zones they are trained, or against mobs of the type that dominate said zone.

I'll use the Vaiyuu as an example. Having been trained in the desert by Dragonslayers it should have an advantage on that type of terrain over something like the Najmok. So it might give an extra buff against dismounting in desert areas like SS and Droughtlands. Either that or it might buff you against dismounts from fire creatures, as SS seems very firey.

The Najmok might buff you against undead dismounts and the IPP mount would be more surefooted in snow, or against water(?) mobs.

Obviously it wouldn't be a 100% buff, as there should be some danger involved with traversing hostile areas.