It is an interesting change for wow powerleveling. Wound poison procs a lot and I would imagine the healing de buffs will not stack. Affix stated, "I am fairly confident (but not 100% sure) that it will be part of the chill effect, not a new de buff." If this is true it will not apply a magical de buff as de buff trash. So it will not help with masking polymorphs. For RMP the main thing that the de buff will do is hurt poison dispel teams by having a permanent mini MS on the target for when wound drops due to abolish/dispel poison about wow powerlevleing.

For example: shamans can not cure poison > NS heal as effectively. If rogues get temporarily peeled the de buff will still limit how quickly the enemy player can be healed up too to get wow gold. However, I think the intent with the design is to bring mages up with melee classes in killing targets by themselves and improving synergy with other classes. The change will help mages separate themselves from rogues and improve relations with warlocks/death knights. I know 2s will not be as important of a factor in the patch to get wow powerleveling, but it significantly improves mage/warlock and mage/priest. In 3s more mage/lock/x and dk/mage/x should appear too.

Using CoC on swaps for the intent of a healing de buff probably will not do much. The rogue swap should apply Wound in only a few swings if not the first. And mages do not do significant damage to multiple targets at once so it will not do much to ms an off target that will be healed up through Wild Growth/POM/Renew etc very easily with or without the de buff. If it is a new magical debuff then it will be very good for every mage comp period about wow powerleveling