Great mod initiative!
A Boers faction would be good indeed. It would give the Brits a modernly equiped opponent.
The challenge with this mod is how can the Brits prevent too much melee and keep the Zulus at a distance. For the Zulus, how can they lure the Brits to leave a defensive position.
The Brits quickly learned after the first disasters and set up (wagon) defences with concentrated fire. The few victories by the Zulus after the Brits changed tactics were mostly skirmishes were the Brits were surprised (as mentioned the French prince was killed in one of them).
A good zulu mod in Napoleon Total War is the Khartoum mod.
The derwishes could be a nice faction too, but than the mod would have to be renamed into British colonial warfare or something