I'm not really sure why the OP has this huge following of Nardo worshippers. Anyhow, a few thoughts:
-Final movie might be alternate reality, or a "what if". It may also be like Movie 5 and be genjutsu.
-Tsunade hasn't been slated yet for the movie. She may die.
-Sasuke's "angst" comes off as semi-justified, given that Naruto himself said so. Also, Sasuke makes some very valid points about the current state of the ninja world. Even Hashirama had to admit the previous Hokage dropped the ball. In Ohnoki's words, the Go-kage "lost themselves" and even Gaara dressed down Ay. Sasuke's desire for revolution is pure and comes from a good set of reasons. The current world that the Sage created has indeed failed in some respects. Given that the human race in NV stands at the brink of extinction, so forced by the Sage's own hand.
-Sasuke's threat comes from the fact that he's equal or more equal to Nardo in terms of power. He also received half the Sage's powers. Nardo himself has confirmed Sauce was at many points in the series far stronger than him. Indra was also known to be as strong or stronger than Ashura. He also just one-shotted all 9 TB at once, including Kurama. The Sage also regards Sasuke as a formidable threat.
-The Great Toad dude also confirms, Sasuke is Naruto's final opponent. PNJ makes this painfully clear. NB has had a pretty clear bias against Sauce since the Go-kage attack arc, but the fact is Sasuke has been stronger than Naruto for most of Shippuden. It's just not something most of Base wants to acknowledge. Though again, Naruto himself stated it multiple times.
My opinion is that Sauce's real threat comes from the fact that TNJ isn't going to cut it. Nardo is going to be forced to stare down some real inconsistencies in Konoha's past and possibly either have to kill his friend, or to save him at the cost of something terrible.
My personal 2 yen:
The TB are gonna die.