Update: The Earth Kingdom is ruled by an Earth Queen in TLOK
Bryan Konietzko has revealed that the current ruler of the Earth Kingdom is an Earth Queen! That’s exciting, but what is possibly more exciting is that this further seems to confirm the notion that Ba Sing Se will be visited in Book 2, or later! This also means that two of the four major nations (The Fire Nation and Earth Kingdom) are ruled by women while the other two (The Water Tribes and United Republic) are ruled by men.
As well as this, it is confirmed that Unalaq’s family is ruling as royal descendants, meaning that Desna, Eska, and him, as well as Korra and her family, are related to Arnook and Princess Yue from Book 1 of ATLA!