Spell Change: Death and Decay!

Greetings. A suggestion for a spell just came in my mind, and I would like to hear everyone's opinion.
Instead of, for example, Ritual of Doom (which is an unuseful spell as it is now) or even as another option instead of Rain of Fire and Hellfire to do shadow AoE damage (I know we have SoC as well, but let me go to the point), why can't we get Death and Decay?

In WC2 Death and Decay was a Death Knight ability, as Death Coil was, and now it is Warlock's one.
In WC3 Death and Decay was Undead's Lich ability
so why no class has it in World of Warcraft?

And I think the most fitting class would be the Warlock.

Now, I'll clear some points of the "effectiveness" of this spell. First, the AoE range I thought is the same as the Teron Gorefiend's one (who did the Shadowmoon quest knows it). Second, the damage it deals is Shadow Damage, which will be good for Affliction warlocks as I am. Third, as Rain of Fire, it will result totally useless in PvP. Fourth, it will work exactly as a sustained shadow dps in AoE, more and less like the Blizzard/Rain of Fire/Hellfire, so if you get away from the area you no longer take damage.

It will be a really useful spell in Instances/Raids, in my humble opinion, instead of a Ritual of Doom spell which is, to be honest, totally unuseful. Moreover, we could get it from a lvl 70 quest (just like the Ritual of Doom) if you want, so Blues, I'm waiting for an answer! :-)

-Nekromoth-