While I don't really think the whole "slap in the face" argument holds much water considering Malfurion isn't really dead and is more or less still in the cooler where he usually is, I do agree there's no need to bring Ysera back after her death in Legion, doubly so in light of the fact that she's still a shade in Shadowlands. Just make Merithra the new Green Aspect in her stead, pass the torch on to a new character, and so forth. Ysera had a good death and a touching denouement, bringing her back to life through this kind of external wizardry just cheapens both stories.