So, consensus is psionic ethergaunts. Reason for yes in my part is that it fits for alien aberration entities to use personal mind magic might (egoistic manner) than depend on sorcery or wizardry which they can view as inferior (like bit like mind flayers do). There are some default ethergaunts who know arcane but they now fall to minority/individualistic entities. So overall question was not customization option but rather make entire specific species more psionic oriented in our setting.