We've changed the Negative Energy spells cast by M'uru and Entropius to no longer cause spell interruption on the target. This should ease the frustration of the encounter for those casting classes who can not obtain 100% resistance to spell interruption through talents and effects such as Concentration Aura.
Having not done the fight myself, I can't really comment on how big of a nerf this is, but it's something, anyway. (Background: M'uru is the next-to-last boss of Sunwell Plateau, followed only by Kil'Jaeden, and Entropius is another aspect of M'uru that appears during the fight.) Guilds who have been wiping on M'uru, or who intend to try him in the future, do you welcome this change?