At first I thought this idea was better than hard to kill. The more I think about it, though, the worse it becomes.
I'll go ahead and say that this idea is worse than dungeon alert, worse than the swing speed nerf, worse than the wing nerf and worse than the nerf to haste. It is unnecessarily complicated and punitive towards players with high dc's. There is no hard cap or DR curve and it reeks of "giving us and idea that you knew that we'd hate, after giving us an idea that you knew we would hate even more," which I, for one, am absolutely sick of.
Please stop it alread with the major game mechanic alterations and give us minor tweaks, like maximum target caps on spells.