I was a firm believer that King would turn out to be a woman. These were my reasons:
- King is covered head to toe, so he's gotta be hiding some big secret (turned out he was hiding his race)
- Wano is the land of the Samurai where women are not allowed to be warriors (turned out to not be true)
- King being a woman would be a hurdle for Zoro to overcome, and a great opportunity for some character developement. Seeing such a strong female swordmaster (turned out not to be the case, technically) would make Zoro remember Kuina and how she threw her life away.
- Through the fight Zoro would grow into a person that is able to go all out against females, King would come to terms with her identity and reveal her true look and fight like that for all to see. And Zoro would come to terms with the fact that his best friend sadly gave her life away for nothing - it would have been possible for her to arrive at the top of world os swordsmen, just like King did.
But eh, it is what it is, I'm not mad with what we got
i was exactly the same opinion about King, but I always went a step further, I hoped and theorized about king being actually Kuina.
i thought she might joined Kaido as payment for security at the island, so he gathered the strongest kids. She then trained to become stronger and overcome every man in the world. So she decided to eat a beast fruit, to get stronger and no man will be able to beat her (except for Kaido). So she lost herself completely in the fear of being beaten by a man. She even called herself then King, to show her dominance and let no one know her „weakness“. She thought her being feminin would be a weakness.
then when Zoro fights her, she first is stronger then him, but he can overcome her because of an open spot, opened by her beast fruit. So Zoro can beat her and tell her, if she would have stayed a woman, he would never be able to beat her.
This could have been a nice story and also a strong statement in direction of feminism.