Since Bannelord is based around the political crises of succession in the Roman Empire, you'd expect that women would have a growing role in these unstable circumstances. I'd imagine that the political infighting between the clans would actually bring them up the social ladder purely due chance or necessity (i.e. your husband died, or you're an important family scrambling to secure influence and status during political transitions).
I agree with the guy who suggested that the number of women involved should remain relatively high, but with sexism mechanics included, like in Warband. That would simulate a world where women from rich families have a chance to fight more actively in the interest of their clan, but still within a patriarchal world.
That's probably the most realistic system. That said, I feel that when it comes to NPC Women, Warband effectively was just as unrealistic as Bannerlord, just in the other direction. (NPC women were marriage fodder or companions and THAT'S IT.) It should still be possible (if not easy) for Women to achieve power, with or without your help, even with the odds against them.
On another note, some common attitudes:
"Women warriors were not a thing!" True, women rarely fought in battle. When they achieved power, it was usually in other ways. However, I think it's often overlooked that nobles fighting in general was uncommon. Yes, they were expected to have martial ability. Yes, there are plenty of recorded instances of them fighting or being killed in battle. However, personal combat was generally something a leader in those times only engaged in as a last resort. Generally, they would hang back and direct their troops from the back line, instead of actively fighting on the front. I am pretty accepting of women in combat in this game for two reasons: one, frontline generals are in general more common in this game then they are, and were, in real life. Two, warriors or no, Women in power did exist in the real middle ages. With Mount and Blade's minimalistic system making it unlikely that a realistic system of women becoming powerful will be implemented, I'm inclined to go "oh well, what can you do?" In regards to them leading troops.
On the other end of the spectrum: "I want Sword Sisters!" I'm actually accepting of there being no Sword Sisters in this game. By not having any type of common troops that are female in the game, Bannerlord does create another type of realism; by making the only women show up be nobles (who have the authority to command troops), and companions (who are twice as useful as the average soldier, which a historical woman generally would have to be to get on the battlefield).
Some people have also claimed it makes no sense from a Lore standpoint for Calradia to be less sexist than Warband. But Lady Isolla's story informs you that Swadia had a history of Warrior Queens. This does provide basis for Vlandia (which is Swadia's predecessor) being more open. There's also Battania, which is based on the Celtic tribes. I'm no expert, but since Boudicca was Celtic, I'm willing to accept Battania (it also helps that they aren't around in Warband, so you can suggest they just had a different culture). As for the Khuzaits, I dunno how they get more sexist over time, but giving women more power (in a general sense, if not necessarily in the sense of having women warriors) makes them a MORE realistic representation of the Mongols they're based on. Historically, medieval Mongolia was one of the least sexist civilizations of the time.