I have some suggestions for rules:
1) No upgrades
2) Factions with HAs of their own (Steppe, Hayasdan, Pahlava, Baktria) can use 2 HAs, other factions can't
3) Only 1 unit of Naked Fanatics (Gaesatae or Tindonatae)

Fell free to make suggestions, to praise it and to annihilate it