Rework "untargetable"

Champions that become "untargetable" should be able to receive damage from AoE spells.

Allow me to explain:

Have you ever played Magic the Gathering? When something is untargetable it means you can't cast anything on it. HOWEVER, AoE spells can still damage the creature because those spells don't technically "target" it.

Shouldn't it be the same here? Fizz jumps on his pole and becomes untargetable. If Brand cast his Pillar of flames, shouldn't the fish get burnt?

Now before you guys down vote this, I said AoE spells. That means single target spells that are skillshots won't have any effect. So in Brands case, his Q and E won't work, but his W can still damage Fizz since he technically never targeted him.

Thoughts?

EDIT: Since there's some confusion on which spells would work; any spell that fully benefits from spell vamp has no effect on someone that's "untargetable".

Champions that leave the screen and come back (Elise, etc) can still maintain their old properties since there's a visual animation that they cannot be reached.