Have you considered allowing drafting units with any of the ancient civics in the scenario? Because we could use the rebellion units setup for this also - I just realized there is a getConscriptUnit callback in CvGameUtils... So drafting units wouldn't cause any Explorers to appear in a pre-gunpowder era. 
Or we could have archery units as the conscript units instead of the default (pre-gunpowder) melee units. On a whole I think drafting would give the scenario a whole new dynamic; the potential for bigger armies - and more wars.

Or we could have archery units as the conscript units instead of the default (pre-gunpowder) melee units. On a whole I think drafting would give the scenario a whole new dynamic; the potential for bigger armies - and more wars.