Before I begin, may I say that I am not the person to consult for anything official, I have a horrendous rating in both OU and the suspect test, but I have been on Showdown for a while. Just not Smogon Forums. Thank you.
I would say to ban Aegislash. If you look throuh the X and Y OU list, for one it is pretty short, and for two, every other pokemon is meant to be a counter to Aegislash. Mandibuzz is a good counter, Bisharp is a good counter, Quagsire is a counter. (eh...?) Entire OU teams are bent around countering Aegislash, if each of your pokemon doesn't have either a noncontact move or a super effective move, you're out of luck for climbing the ladder. Due to this, almost every OU team is the same. Really, a ban to Aegislash would shake up the game. Pokemon like Assault Vest Conkelldurr would see more usage, pokemon like Hawlucha would be viable, (Really, only one decent Aegislash killing move?) pokemon that are of types like Fairy or Ghost would see more usage. Maybe Mega Tyranitar or Alakazam would be more viable. In short, you would see a lot more unique pokemon if Aegislash was banned from OU.
My second point is that, due to Stance Change, Aegi has a pseudo 720 BST. This is tied with Arceus for the highest non-mega BST of ALL POKEMON. Even Ubers. The only pokes that have higher are the two M-Mewtwos. If that doesn't put it in Ubers, idk what does.
My third statement is about Kings Shield. This move, for those that don't know (Mainly all of the people who say Aegi should stay) is exactly like Protect, except it halves the attackers Atk if it blocks a contact move. This means that if you try to use Knock Off to slap off its Leftovers or Weakness Policy (Which activates before it gets knocked off) then you either get killed because of your attack drop or switch and get killed by Shadow Ball (There arent Normal ypes in OU.) Kings Shield has priority, so any pokemon that doesnt get an attack drop has to deal with Shield Forme on the next turn due to its terrible speed, and then it uses Priority Kings Shield the next turn. You never get the chance to attack Blade Forme. This is a game breaking move. If you dont ban Aegislash, ban Kings Shield.
For all of you whining about losing your shiny new toy, just use Doublade. It can run Eviolite and has a half decent Atk stat that you can use Swords Dance with. I have one that I use in X and Y that owns with Gyro Ball. With that, I'm done.