So after some thinking, I am under the impression that Fateweaver could be our biggest boost right now. Imagining 1KSons and Plague Marines with re-rolls on their saves is awesome. I think I may have to take a unit of 10x IoT Terminators to try out how resilient a 2+/4++ with re-rolls can be, especially with how hard AP2 Close Combat weapons are to come by right now. IoT Terminators will be better then TH/SS terminators, and they can shoot!
Fateweaver is also a flying MC so he has high mobility after he hits the table. And with his rules of Master of Sorcery and We Are Legion, he can effectively threaten 3 units a turn. Imagine throwing a Bolt of Tzeench at a tank, Wind of chaos at a unit of Terminators, and Daemonic Gaze as some Marines, then getting to assault the tank and use SMASH! It just sounds like a lot of fun to me.