[PapaBear3625]

Since the death of Ibn Saud in 1953, the crown has always gone to one of his sons. Therefore you can be certain Abdullah’s successor will be a brother or half-brother. I don’t expect that to change until the last son of Ibn Saud dies.

Which means the kingship will be held by increasingly old men.

There's also the issue of the increasing size of the royal family. Looking through the list of princes in the wiki "line of succession" page, they generally have 10 or more children, each of whom presumably want to have the same opulent lifestyle as their dad. Meanwhile, oil revenue is NOT increasing by an order of magnitude each generation.

[Berosus]

Back when it was called Siam, Thailand had the same problem with a growing royal family. Thus, when they revamped the Siamese law code in the fifteenth century, they declared that if you were separated from the current king by five or more generations, you were no longer part of the royal family. That worked until the twentieth century, when the kings stopped practicing polygamy and the royal family shrank. To fix that problem, a new law was added saying the crown could pass to women as well as men.

Maybe it’s time for the Saudis to lay down their rules of succession, too.