I thought that the SoSS was a good choice as well, but Malekith's weapon "The Destroyer" that can destroy a random magic item (with a 4+ roll) on any successful HIT, is what concerns me. So making it harder for him to land those hits (4+ instead of 3+) might be a better option. It would be game over if that VHS is destroyed before you get to use it.
My armies: Empire, Dwarfs, High Elves, Wood Elves, Dark Elves, Lizardmen, Skaven, Tomb Kings, Ogre Kingdoms, Orcs and Goblins, and Skitarii (40K).
He doesn't pack Destroyer in the End Times (at least in Khaine anyway, I'm not totally familiar with it all)
Destroyer certainly would put that at risk though with him hitting first, all the more reason to take ASF sword so you hit at the same time. But I guess this is a less viable strategy against non-combined profile Malekith because you don't get the 10 attacks or Strength/Toughness 6.