Picture this anons. Inside the vault Vashtorr is looking for, tearing apart reality in the process as Wyrmwood burrows through space and time, is a sealed Warp power. The Old Ones seeing the chaos the War in Heaven caused in the Warp, used their dimished powers to seal one of the emotional parasites while it was on the cusp of self awareness and then when the vault opens it return to its spot before growing to be a new Chaos God. And we can finally have a yellow themed chaos god. Since I don't think GW want the Emperor, despite his love of gold, as he is now to be a chaos god