Charge more horses per mounted unit upgrade troop size.
Oh, and caravans. Give players an ability to "upgrade" caravans with up to 2 mounts.
This means your 2 Wargs or Warhorses are "pulling" the wagon and will defend it if attacked. Each time a wagon departs, you may pay up to 2 or 4 mounts to "protect" it.
If the caravan is attacked, it would simulate an auto-battle, and the mounts would increase the strength of the caravan.
Lastly, Legacy of Serrane could give more defense for caravans.
When a caravan is defeated, it remains on the map and rolls for survival. If it fails, the caravan is destroyed, if it did then the caravan is assumed to have survived.
Caravan Escort would add a new dimension to the game, and would be more than fun for everyone.