In update 1.23, the one released alongside Cradle of Civilization, advisors were given personal religions and cultures and the ability to be upgraded. It seems like I can almost never upgrade an advisor though. I've seen it a few times, but right now I can't upgrade any of them.
The changelog says that they must be of a promoted or same-group culture, and all of my advisors are of my primary culture, but the button isn't showing up still. Is there another requirement for promoting advisors or am I misunderstanding something?