BrM spell mitigation also got nerfed along with other tanks. Our spell damage stagger is only at 20% in BfA, down from our current 40% and stagger itself has been nerfed for 5%. So in BfA we're only going to stagger 20% of 70% = 14% of spell damage.... Even with every talent set for spell damage mitigation, it'll still only be 28% of 80% stagger = 22.4% spell damage mitigation.
I'd still rather have the self healing from DK/DH over our 14% to 22% spell stagger.