I believe this is referring to some of the Mythic Gul'dan stuff but I can't say for certain. I don't think people were violating rules, rather they created something clever that Blizzard didn't think of, and it went beyond what Blizzard thought was possible.
They are referin to mythic star augur Weak auras. As soon as you enter his room WA turns friendly name plates on. During the encounter when ppl get celestial mark (mythic ability) above their heads WA displays green and red colored square. You now only need to get to other person with green square as red ones are a no go. So WA makes this extremly easy as you dont need to specifcly search for another player with your sign (wolf etc). You onlt need to run to other person with green square and avoid red oned. This WA attach the square to the friendly nameplates which is why they are disabling them in future raids.
Comment by Ysysys
This is a terrible change. I dont see a big difference of the accused addons to the visiual appearance that Blizz is providing anyway already in these specific raids. A symbol pops up on the player and they have to find each other. Wow. Now the symbol is displayed with a different icon. Such wow, such game breaking.
But to destroy all the none game breaking usefulness to all other players because of a small raiding portion on a single encounter is just disgusting! Especially when they still let PvPers see the buffs currently active on friendly players. I want to see these buffs in mythic dungeons aswell. I used these nameplates displays to learn when people pop their cooldown, when I have Hots on them, or simply for specific debuffs. It made me learn alot! So they are again missing the point that these addons made friendly player bars finally after all those years somehow useful.
So if you want to break these addons that make your &*!@ty friendly player bar finally somehow useful, then provide the same means first to us, which means the possibility to hide your terrible friendly player bars, which are a completely idiotic cluster!@#$ and unuseful, with a clickthrough mechanic while still showing the buffs/debuffs currently active on players, OR dont break it just like that at all.