The history of Konoha and the hypocrisy of the 1st Hokage
So far we got what the scroll was, who the ones that know everything are and what Sasuke is now after. The obvious confirmation that Hiruzen was basically a douchebag, hypocrite (notice Orochimaru used terms like this against him a LOT) and was responsible for and ordered Itachi to murder his own family.
We see that the Senju are not the "good" guys and the Uchiha are not the "bad" guys. Kisihimoto just threw moral ambiguity back in the mix, showing that Tobirama went against even his own brother's dying wishes to persecute the Uchiha and that his idiotic pride brought about the forbidden jutsu Edo Tensei and ultimately pursued policies that led to the rise of a "new Madara" in the form of Obito and villains like Kabuto and Orochimaru. The 2nd did not end wars as the 1st wanted but instead presided of the 2nd and 3rd great Ninja wars as a nationalistic nutcase. Tobirama is essentially Narutoverse's Hitler.
Central questions remaining to be answered in Sasuke-Orochimaru arc:
1) What is the village an what are shinobi?
2) What happened between Hashirama and Madara, why did Izuna die?
3) Why did Orochimaru want to really crush the leaf?
4) How will Sasuke react to these revelations, and how will Minato react to being used to fight Naruto?
5) What role will the Edo-kage play in the future of the series?
Regarding the first answer and second answers, I think we will get a 1-2 chapter flashback regarding Hashi, Izuna and Madara. This will essentially focus on Madara's backstory and how Madara awoken the Mangekyou and why he became such an evil sadistic bastard. It will obviously have to do with why he took Izuna's eyes. Hashirama will probably reveal how he died and ultimately reveal that Madara became stronger and killed him before he could tell the village Madara was still alive. This battle probably drained most of Madara's remaining EMS-powers and left him with Hashirama's DNA (how else did Madara manage to get Hashirama cells?) We will get some hints of a gay bromance between Hashirama and Madara, and that ultimately Madara didn't mean to kill him or some corny thing like that. This is hinted at when Madara says he would have taught Hashirama to resurrect himself (that's the literal Japanese translation). Using Hashirama's cells, he created Zetsu and then the Obito backstory we saw already. Hashirama will reveal that Konoha was founded with the idea of taking care of everyone as a community and to strengthen the nations.
As for the remaining answers, I think we will get that Orochimaru had a huge problem with the village. Bigger than Madara's even, he wanted to crush Konoha and the ideas it represented. Orochimaru will give Sasuke the other side of the coin. Look at what Hashirama's well-meaning communalism and Tobirama's feudalism have done to the ninja world. It's made people like Itachi mere tools used to serve their whims. Their egos, to serve THEM. At this point Sasuke rebukes all four Hokage as fools and rejects Konoha entirely, siding with Orochimaru. Oro uses this moment to attack Sasuke. He will overwrite Tobi-rama's personality in this second, send Minato to "kill naruto" and keep Hiruzen as his own zombie slave.
Flashback to main battle:
Madara's the end result after Orochimaru says "the selfishness of ninja". Obito kicks the bucket after a short-fight with Kakashi and Guy. He tells them to stop Madara and make Rin's death count for something. Kakashi may or may not get the other Obito eye. Madara reveals he merely used Obito and he killed Rin. He reveals he didn't even need Obito since arriving here and shows his previously mentioned self-resurrection technique. Madara essentially uses Rinne Tensei to revive himself bypassing restrictions with Hashirama cells. The fight against the Juubi (now fully under Madara's control) goes far less smoothly. A lot of fodder ninja die. Probably we get Tsunade's death in here and possibly someone like Shino.
Naruto with BM and SM at the same time appears on the verge of beating Madara with his friends help, but then the cavalry arrives. Jugo and Suigetsu jump in against some remaining fodder K11. We see that Orochimaru appears to be in control of Sasuke's body, and fires a Chidori senbon that kills Sakura almost instantly. Naruto looks back and doesn't make it in time except to catch her lifeless body. Before Naruto can react, Edo-Minato seals Kyuubi back into Naruto and Naruto falls. We get another inner-Naruto world discussion with him and Kurama . This time S06P shows up. Kyuubi and possibly Juubi will be sealed inside Naruto
Madara regenerates and begins fighting Oro-Sasuke. Ultimately Madara is beaten by Edo Hashirama, who then having beaten his life-long rival is able to find peace. Minato and Naruto fight elsewhere and Naruto eventually seals his father with "THAT TECHNIQUE" which will end up being some lame Uzumaki sealing jutsu that's absurdly overpowered. Oro-Sasuke flashback, where we see Sasuke offer his body to Orochimaru in exchange for access to the Hashirama cells (knowing he can unlock Rinnegan this way). We think Orochimaru is in control, but really Sasuke had him under genjutsu before the body absorbption technique. Orochimaru-Zetsu is permanently sealed inside Sasuke, and Sasuke accesses his power sans curse mark.
Oro-Sasuke with Rinnegan vs. BM Naruto will be the final major battle of the series