I've always thought a vehicle system like WOW would work for mounted combat in ESO. Specifically in Cyro have horses you can "rent" for AP that you can ride around, have their own set of skills + ulti that are baked in and cant be changed but perhaps morphed as part of a mounted combat skill line in the Alliance War category. Have it so if you sprint into players they get knocked back etc for crowd control purposes and so on.
dyable mount armour wouldn't go a miss that's for sure. Keep the mounts base colours but let us change the saddle, armour bag colours etc.