I was just wondering where that came from. Whenever I saw promo art on the official AC and Ubisoft websites it was always Alexios. Even the DLC shows him. So wouldn't that make Alexios the canon playable character? It would make sense given how in reality women in most of Greece were treated terribly and married women weren't allowed to leave their homes witout their husbands and had to wear viels, while the Persians were more egalitarian, so Darius would be OK with Neema being an active female assassin. Though Spartan's were almost as egalitarian as the Persians. I'm just saying, Kassandra wouldn't be able to command any respect or be treated as a normal human being by almost all of the Greek world, where Neema (appears if Alexios is pc) would come from a culture that views women in a more equal light to men so there would be no problem with her escapades from family.
But then again, this game is full of revisionist history. Like the lack of Spartan women wearing chitoniskos and competing with the men in the Spartan sports games. There was a massive lack of slaves, most Spartan inhabitants were slaves, why they would slaughter their slaves every once in awhile. Kassandra/Alexios also wouldn't be considered Spartan citizens until they took the citizenship exam that's required for all Spartan born individuals to take, and pass, or else they'd become a slave after turning 18. Then the children, they're wearing clothing. A lot of Greeks didn't dress their children until they reached a young age (I get why they didn't do that and left out the gymnopedia and I think that decision is for the best).
That's only the tip of the iceberg, but I guess if they're kind of rewritting history it would be ok to have a female canon character. I don't know, what do you guys think?
This has been an issue of confusion since the game came out, however Kassandra's 'canon' status came from the novelization of the game and was the further supported by the Assassin's Creed: The Essential Guide and other non-fiction sources all identifying Kassandra as "The Eagle-Bearing misthios".