Well we never saw madara did amaterasu..before when he finally appeared i thought he can do amaterasu as goddamn senior of the uchiha clan..he must have unveiled all the secret of uchiha eyes until rinnegan yet he can't do amaterasu...when he had susanoo i asked when he will bring amaterasu to the table?..but he never showed it and with the things going on it appears that he can't do it. And if he can't do it does it mean he doesn't have knowledge of generating black fire?..whereas itachi and tobi know about it!?!..so he must have knowledge about it.And if he knows about it why can't he do it of such power level?...this just shows itachi's brilliance of giving birth to amaterasu.
Also if it happens that he can use amaterasu which must have been really possible only that kishi did not grant it, what impact do you think will it have in this war? For me I think this war would have been over now with madara's victory or if not many important characters and some kages are dead already..wanna know your thoughts guys!?..thank you!