Just an idea on a way to reward "elite" players for finishing heroic content before nerfs, Give a certain time limit for the HEROIC boss's to be killed, say 4 to 5 months then nerf, Each boss they kill before the nerf could give an achievement and/or a cosmetic reward to the group that kills it before the nerf. Gives bragging rights to "elite" guilds and gives players a challenge to try and finish progression before nerf.