There is a saying in homelitics (the study of sermons and preaching) that you should not attempt to put all you know into one sermon... you just might succeed.
Not that you've done that here, but the article is so full of threads, some complimentary, some competing, some vague, that it's hard to pull out exactly what you mean. There's meat here for several, smaller but concise, articles on a range of topics. (And, speaking personally, any attempt to buttress an argument using Game Of Thrones handicaps that argument quite a bit. )
--Elites' is a vague word , it can be used to describe a highly stratified self-appointed, oligarchy or a true meritocracy where elite is defined more or less objectively. I think what you mean--and you do address it it in the piece when you point out the disparity in voting requirements/needs vis a vis Democrats n Republicans--is that Conservative elites don't want you to vote. This is a crucial distinction. Progressive elites (such as they are...) want more and more people to vote.
-Comparison between the slavery as practiced in Plato's time and that of Thomas Jefferson is problematic because Plato's slavery wasn't color-bound: anyone could be a slave, and often in the position by circumstance of being on the losing side of a war. Plato could have become a slave himself if Sparta had done better in the Peloponnesian Wars. There was never any chance that Thomas Jefferson was going to be enslaved. This doesn't justify either system of slavery, but does provide for different and differing perspectives from those invested in each system.
--And you should spare some time to look closer at John Stuart Mill not least because he is the first published feminist: arguing for political involvement for women before anybody else.
While the article to which you link is attempting to point out that John Stuart Mill's defense of 'plural voting' is at odds with his overall theory of democracy--and it is--I'll briefly take it as read and say that it still doesn't rise to the level of 'elites' since the predicate for 'more votes' doesn't derive from artibrary metric but a level of education, theoretically attainable to any and every person. Second order democracy, if you will. Nor is addressed the possible incentives this could have: if getting more education got you more power, in a directly measurable way a la John Stuart Mill, then more people would get more education. A theoretical win/win