I mean an era system like RTR...In this great mod roman army changes and former types of units just simply don't exist.I think that's the way this mod should follow...for example in the 1st era 1071-1200 should not exist knight units whith semi partial plate armors...After 1200 a player should recruit only new type of wariors and so on.An other ex. are the sergeants.They are exist in the 1st era but in the 2nd there must be new types like men at arms....For byzantine empire a player could have katafraktoi in the 1st era but not in the 2nd or at least the 3rd.Pronoiaroi should take their place in the empire's unit roster.
It is just an idea...