I dont see how he gets stronger than the ems. Also the point you forget is its impossible to beat juubi edo madara and obito w.o sasuke allying himself with the shinobi army. He could use the hokages, but even they would struggle w.o naruto and co. The 10 tails is a huge deal.Sasuke will change but I seriously doubt it will be a good change. The look on Sasuke's face says that he is just getting angrier.
This is just me but I think he goes to the battlefield with the Hokage and acts as a third side turning the war into a three way.
I think that Sasuke decides to kill not only Naruto and the people of the Hidden Leaf but Obito and Madara as well (or at least he will try).
Also it was said that the Sharingan gets stronger as one is more filled with hate.
I think that by the time this is over Sasuke will be angrier and more evil then ever.
It would be easy if minato could remember the past as he talks to sasuke i suppose.I agree with your point and hope it will happen. On the other hand however what questions will he ask that would bring up Naruto's family and the fact that Kushina and Mikoto were friends? Especially since Minato would not have known Sasuke for very long, at most a few months, since he and Kushina both died when Sasuke was an infant.
Sasuke hasnt got what it takes to kill all shinobi, edo madara, obito and most of these 4 hokage beat him, sorry. Thats why hell have to make an alliance for a while.I think sasuke will decide to not only destroy kohona but all shinobi and hokage naruto will have to stop him.