If I recall correctly, it was two questions:
-"Can a good man be King?"
-"Can a people of an advance society actually accept a monarchy?"
The first question, I suspect, is based on T'Challa controversial decisions during the Hickman run. Coates often mentioned in particular T'Challa deciding to not use the bomb in New Avengers #21 to destroy a populated world, despite T'Chaka and the rest of T'Challa's ancestors insisting and reminding him that it was the only way to save Wakanda and his own world. T'Challa chooses not to use it and T'Chaka and his ancestors disown him.
Coates' apparent conclusion: T'Challa is a good man who wants to do the right thing, but his morals prevent him to go all the way, something kings have to do.
The second question has more to do with Coates' stance on monarchies if anything. Monarchies are one of, if not, the oldest forms of governments known to man. In Coates's mind, why would the most advanced civilization on Earth accept such an old-fashioned government, despite its drawbacks?
Coates' apparent conclusion: Citizens of an advanced nation cannot accept a monarchy. Wakanda, it appears, will move on to a new form of government.
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Hoping this brings some clarity, cuz even I'm not too sure that's the actual path to an end game. I'm just speculating out chea.