So this is my first post here, but I do have a quite a bit of battling experience in a different nick in both Shoddy and PO; so take what I say with a grain of salt.
Aegis is a quite difficult suspect. It has an unique role, and influences the metagame in a quite different way. While I have not read all of this conversation, I feel the need to emphasize a little bit on some of the pro ban arguments.
About the KS 50/50 argument, a lot of people are saying that anything with a setup move can take advantage of. But doesn't it go both ways? while opponent can either setup, attack or switch; aegis too can either KS, attack or switch in appropriate counter for free. The difference is simply that in case of wrong prediction, the aegis user doesn't risk getting -2 attack. Every time aegis uses king shield, at the very list he scouts the opponent and reverts back to his behemoth 150/150 defense form. Aegis invites the opponent to a poker game while tipping the dealer to always give him a pairs at the beginning. Sure he could still lose, but its a game where he has the better odds. There's also the point that it kills momentum like no other. Say a landorus-T is facing aegis, and aegis has a teammate in Latios. Now Latios can pretty much come in for free on the first turn, because if Lando-T uturns, and aegis kS, then Lando-T gets -2 attack and therefore no longer counter Aegis who can fire SB without problem. If lando-T user does not want to take that risk and eqs; then either Latios will come in for free(and take the momentum in his hand) or Aegis will just KS and get a bit of leftover recovery. Only case Lando-T has any advantage is Latios comes in and lando-T u turns. So to me, the 50/50's we talk about seems more like 60/40 in favor of aegis.
Now onto the over centralizing argument. Aegis is not only the poke that asks the question why you are not using it, but it is the poke which dictates what works and what does not in this metagame. D-nite(which is among the least changed pokes this gen from BW) using eq is a pretty poor example of how Aegis forces pokes to run sub-optimal coverage. Why does Pinsir run eq, a move with 20 less base power than CC and makes him hard walled by Skarm, and cant hit Rotom-W neutrally? That's because getting past a poke who is not only available in more teams than not, but could potentially lower its attack is much more important than breaking through game's one of the best physical walls. With the nerf to steel and rise of talon, you'd think choice T-tar wouldnt be out of flavor. But despite hitting Aegis super effectively this gen which would not be the case had it existed last gen, it is not advisable to spam crunch against aegis. Sp.def gliscor would be a gimmick if aegis did not exist. Despite the relative lack of resistance, here we have mandibuzz rising from NU to OU. Why? Because it stops most of aegis sets. Why is a poke with 200 base atk, 100 base speed and powerful stab not OU? because OU is ruled by aegis. Ask yourselves, should a single pokemon (S rank or not) have this much impact on a metagame? 8 months of playing in this tier have us used to using and preparing for aegis. This should not mean its easier to handle or it should stay in the tier.
Next up is versatility. It can not only defeat each and every single of its counter or checks via different sets without resorting to gimmick, but also can fill in pretty much every single steel and ghost type's shoes. Tank, wallbreaker, midgame sweeper, pivot...pretty much any role other than choice attacker can be fulfilled by aegis at a reasonable effectiveness without compromising its basic qualities. That's how good Aegis is.
Finally, base stats. Only thing I'd like to point out here is that while Aegis do not always have 720 base stats, its low speed means it usually uses all of his 720 stats in a specific turn. Most of those who are slower than aegis is incapable of doing much even in blade form. That leaves only Conkderp and foul play amoonguss, the former of which has to take a guessing game against aegis.
While I'm not entirely sure whether Aegis deserves to go, I doubt it will be in the best interest of the OU metagame to let it continue. So for now I am leaning towards BAN.
Oh, and sorry for the wall of text.