@Yuvell the problem with adding one of Qiyana's sisters as a champ is that she hates them. She's willing to kill them in order to get the throne and even exposed one of her sister's towns that she was supposed to protect in order to become the protector. And while they did add Yone, who has a lot of similarities with Yasuo, adding one of her sisters would cause a big overlap in design, I'm sure. And also, she is stated to be the strongest of her sisters, so if they wanted to keep the lore straight they would have to either make them weaker than Qiyana, or have them have a completely different kit that goes against the lore. So, imo, adding one of Qiyana's sisters as a champ is unlikely.
I think if they want to add more champs from Ixtal they should come up with something original.
I remember I came up with a champ idea, based on and has the same name as Gellir, from Norse mythology, and if you know anything about him it would make sense from him to be from Ixtal.