Disclaimer: If you don't read the whole thing, then don't bother posting because it pisses me off when someone posts some stupid claim that I already addressed in the OP (without giving some reason that actually relates or goes against my reason in the OP).
I think that one person's theory which stated that the producers didn't want to spoil things for the anime only viewers is actually correct. Here is why:
The movie actually neglected to touch on so many important plot points that you'd think would be mentioned. "Coincidentally" enough, these omitted plot points are all things that have not yet happened or been revealed in the anime (nor had they happened on December 6th when the movie released in Japan). Here are some of those neglected plot points:
1. In the beginning of the movie, the narrator gave a brief history of the shinobi world starting from Kaguya eating the fruit to Naruto vs Sasuke (final battle). However, the movie just stated that Kaguya ate the fruit and became the first to wield chakara, and that over time humanity became greedy for power and continued to fight. It did mention that Hagoromo fought the juubi, but it neglected to mention that Kaguya fused with the shinju to become the juubi in order to take away her sons' chakara, or the fact that Kaguya trapped nations under the infinite tsukuyomi and turned them into white zetsus, or the fact that Hamura helped fight the juubi, or even the fact that Kaguya created Black Zetsu who then manipulated the events of the shinobi world in order to bring about Kaguya's revival. If one is trying to explain the history of the shinobi world, then one should know that the actions of Kaguya and the manipulation of Black Zetsu are actually crucial aspects of shinobi history. They are not to be neglected. If it wasn't for Kaguya and Black Zetsu, then the juubi wouldn't exist in the first place, there would have never been an infinite tsukuyomi, there would have never been that centuries long war between the Uchiha and Senju and there would have been no eye of the moon plan. Therefore, you can not say that these aspects were not important and that this is why they weren't mentioned.
2. It showed Indra and Asura, but it did not mention them by name. Furthermore, it showed Hashirama fighting Madara and Naruto/Sasuke charging at each other, but it neglected to mention that both Hashirama/Madara's fight and Naruto/Sasuke's fight related to Indra/Asura's in that the former two pairs are the transmigrants of the latter. This conflict between Indra and Asura was the foundation of one of the pivotal themes of the series (the method by which peace should be brought to the world; love or power?) and a pivotal conflict in the history of the shinobi world (causing a war that lasted for centuries and eventually led to the founding of hidden villages). Therefore, it was an important plot point that is crucial to explaining the history of the shinobi world.
3. It neglected to mention Hagoromo transcending time and giving Naruto/Sasuke powerups, Madara casting the infinite tsukuyomi, Kaguya's revival and then her/Black Zetsu's subsequent sealing away in another dimension. These were quite important moments that you'd think would be in a cinematic like this. Also, it is important to note that later in the movie, Toneri was telling Hinata about the bad things that humans have done with chakara. He mentioned the mazou getting stolen. He mentioned war breaking out. He mentioned the juubi being revived. Yet he still neglected to mention the infinite tsukuyomi getting casted (which because of the whole white zetsu thing, is arguably worse than any of the aforementioned things since it literally brought about what would have been the apocalypse if it wasn't for team 7 and Obito).
4. Finally, the opening cinematic neglects to showcase the outcome of Naruto vs. Sasuke or the releasing of the infinite tsukuyomi. It only shows the statues making the harmony symbol.
Now all of these plot points are very pivotal points in shinobi history that one wouldn't normally exclude when explaining shinobi history. Furthermore, when trying to convince someone that humanity is using chakara for evil, you'd think that mentioning the casting of an apocalyptic genjutsu would be one of the main things that you mention to prove your point. Does either the cinematic or Toneri mention any of this? No!
Now what does all of these points have in common? The answer is:
The anime has not yet reached the points of these revelations/events! There is no other feasible reason not to include such things.
Now some people might be thinking: "This theory is wrong because the movie did spoil Sasuke's rinnegan, the fact that Kakashi lost his sharingan and became the 6th hokage, and the fact that Naruto vs. Sasuke happened".
Here is what I have to say to that:
1. Sasuke getting the rinnegan has been foreshadowed for years (ever since chapter 560 when Madara first showcased it and revealed that he awakened it just before his death after getting Hashirama's DNA). Despite the fact that at that time we thought you just needed Uchiha and Senju DNA (as opposed to Indra's and Asura's chakaras), we as the fan base still started immediately coming up with theories as to how Sasuke would get Senju DNA and awaken rinnegan. You don't believe me? Go back and watch the youtuber Sawyer7mage's review of chapter 560. You'll see that people way back when were already predicting that Sasuke would get rinnegan. If you want a more recent example, when Hashirama gave Sasuke that chakara for that jutsu that was supposed to be able to bind Madara, debates even on this base alone were going on and on that this would awaken the rinnegan for Sasuke. Sasuke fans then had a field day when Kabuto came and gave Sasuke Hashirama's cells. Face it, showing Sasuke's rinnegan in the Last is no spoiler. It has been foreshadowed for years. Besides, the movie didn't showcase amenotejikara, or the 6 tomoes in his rinnegan, nor did it explain how he got it or why he only had one. Basically, the movie spoiled nothing about this.
2. Kakashi becoming hokage is something that could have easily been expected. It has been touched on multiple times in the series. Movie watchers would probably just figure that Tsunade just got tired of the job one day and gave it to Kakashi. It is not that big of a revelation. As for losing his sharingan, I'll admit that this one is hard to justify, but it is still not that big of a spoiler as it doesn't reveal exactly how or when Kakashi lost it. Considering that Kakashi was not the focus of the movie, many fans probably weren't even paying attention to that small detail anyway.
3. I don't care if you are an anime only viewer or not. If you didn't see Naruto vs. Sasuke coming then you are just slow. There have been multiple OVAs about this. Numerous openings/endings of the anime have showcased this. In just about every ninja storm game there is a Naruto vs. Sasuke boss battle (even at times such as the 5 kage summit arc where they didn't really have a full on fight. They just clashed rasengan and chidori). The fight has been foreshadowed in the manga/anime (by the toad's prophecy that Naruto would fight a young man whose power lies in his eyes, by Naruto's statement that he and Sasuke would both die if they fought, by Naruto and Sasuke sizing up each other's power when they met during the war, etc...) This was no spoiler. Besides, it did not show the outcome of the fight, so it really did spoil nothing.
Clearly the movie was avoiding the spoiling of very pivotal plot points. Naruto gaining RSM was one of said plot points. It makes sense therefore, that it did not appear in the movie.
That is all I have to say.
