EU-Rome had this too, in the form of laws category. It was awkwardly implemented (and only for limited nations) but it was there.
I think this time it should be present everywhere but restricted based on culture/religion. For example Indian women had pretty much every right except military service outside of bodyguards and succession preference over sons during this time...on the other spectrum Greek women (even those living in India) were not allowed to have any private property without a son/husband/father/uncle managing it and weren't allowed near public offices. Roman women had moderate rights that improved much over centuries, but were still forbidden from government and everything related regardless of their wealth. Persian women had property rights but otherwise everything was controlled by their family. The game can depict the entire range between these two.
So, succession laws should be there, but enacting them would have certain religious requirements. Like CK2 there should be 5 laws from one degree of extremity to another - from Agnatic (strict male only/Graeco-Roman), Agnatic-Cognatic (male preference/Indian), Absolute Cognatic (equal gender/Egyptian and tribal), Enatic-Cognatic (female preference/matriarchal tribal states in parts of Europe) and finally Enatic (strict female only/Amazon).
And like CK2 required you to be Basque or Cathar/Messalian to switch beyond historical succession types, same can be made here using culture or religion. The requirements can then be modded.
This way, modders can unlock the successions for all if they wish (for example for female Roman consuls if needed), while the actual game keeps it completely historical.
