Poppers whole theory on open and closed societies was that open societies have some sort of mechanism to change who is in power without a violent revolution or a war.

I am not sure I know what Plato envisioned as a society, but his strict division between intellectual and working class seems like a receipe to disaster. Two or three generations in nothing would have been left of the potential advantages of putting the intellectuals in power, because their sons would've taken that power for granted and soon you would've ended up with an ordinary aristocracy.

Granted, those were other times — slavery was totally common for example. But I still think Popper has the better take on how to organize power and who knows, maybe Plato would have agreed if he had the chance to read Popper.