So... Basically you spent a lot of time on another thread, and since nobody wanted to read it, you are posting the link again? Sadly it will make people rage even more, though I've always had Shisui high at my list of candidates, though I think he is pretty much dead... How else did Itachi get MS?
More importantly I don't follow, how Shisui could be the key to taking over the war, or whatever. IMO it has to be Madara and Izuna. Izuna will tell sasuke the truth, and sasuke will want to fight Madara.
Why else did Kishi hide all of Madaras MS abilities as well as hiding the perfect susanoo? It's so obvious I could cry..
Madara vs Sasuke will happen. We need to see the first ever EMS vs EMS , PS vs PS, etc. fight. And it will be... wait for it... keep waiting....
Anyway if it's them it explains everything that has been said so far, and it would tell Sasuke what his clan really wanted, and if Madaras desire (which atm is the same desire as Sasukes), is what his answer should be. And only Izuna can probably tell him this. Shisui only knows of the planned coup, but knowing why the coup started, why they should be a part of a village, and what to do with his brothers eyes, he needs to meet Izuna U_U none other can tell him