I've got an idea for an interesting mechanic for a couple of dark elf units, whenever they are added. (although the mechanic could work for anyone)
Dragoon Archer (needs beter name)
3 moves, 5 strength
Can be just like the regular horse archer units
Shadow Archer
1 move, 6 strength
Can be just like the regular longbowman units
The Dragoon Archer (mounted unit) has the special ability to dismount from the horses and become a Shadow Archer
This new Archer unit is then stronger, and better equiped to defend citys & terrain.
The Shadow Archer (archer unit) can mount horses if it has them available to it. This converts it into a Dragoon Archer unit with lower base strength but more movement.
Either mounting or dismounting should take the units attack for the turn. (unless it has blitz)
The conversion would take the technology required to make the other unit, of course.
This would add an interesting synergy between the archery tech line and the horsmanship tech line.
Such a mobile defense force would be very usefull at times.