MagisterCultuum
Great Sage
One wonders whether you would even want to have a seperate mounted line if you have mount promotions. Xienwolf said it would be possible for promotions (like mounts) to change a unit's unitcombat, so regular disciple/melee/archer/recon units could become mounted units (gaining movement at the cost of loose their terrain defenses) by selecting a mount. I guess Chariots would probably always have to be mounted units (the cart isn't very useful on its own), but Knight could become powerful Melee units who could become more powerful and mobile attackers by taking their mounts or dismount to defend better and horse archers would just be archers/longbowmen/crossbowmen who have taken mounts.