I always want to talk about this film. Now that I am a member in here, time to say what's in my head.
From the start, I was wondering about that first poster due to characters being "opposite". So, AU came to mind. Then, the plot was revealed and now it's becoming clearer. This could be a movie that shows "what if" scenario, while making something new from Kishi. That said I am definitely looking forward to the film because he's writing it and he could bring some nice creative ideas.
Now about Naruto and Sakura being trapped in genjutsu, I don't want to get too excited but it's definitely promising. I am going to drift off from the movie for a moment and talk about NaruSaku and Sakura's role.
1) Yes, movie is considered filler, but this is made by Kishi. It is not related, BUT if he writes couple to plenty of NaruSaku scenes, then that screams which pairing he favors the most. Remember, he's taking an advantage of AU and genjutsu, so he don't have to worry about exploiting the outcome of the pairing. Granted, he's not going to make it canon, but he can have them hinting and such (prior to hug and such). As if all other previous films doesn't have NaruSaku moments, now this one can be done by the original maker. I can't guarantee that he's going to implement some, but we shall wait for more info. Funny to me, but did someone got a good feeling with that second poster? As in Sakura next to Naruto's parents. I sense they did it intentional.
2) Now, about Sakura's role. NaruSaku moments would be sweet, but her role as in fighting or play smart is something I hope to see. Now, I really do feel that Kishi will have her do some good stuff and play a big role. There are evidences that signify her role to be in the main cast. First off, anyone seen the poster listing for main characters? It listed Naruto (duh

), Minato (NICE!), and Sakura. Why is she listed? Because it's highly likely that she is the main character of the film. I went back to last film poster and it didn't list her. In fact, it didn't list anyone. The main site listed two new characters and Naruto. If that's the case, then that means Sakura is going to play a big role. Second, the second poster shows her again, which again, signify her role in the movie. You can say "Well they do that because of Team 7". That's fine, but synopsis clearly stated her role or at least how she is caught into the situation. Lastly, remember the sketches, why show Naruto and Sakura (ignore new characters sketches for now) sketches. Two of them only. Well, that should tell you that they're the main cast in the film. Most likely, we going to see all sketches of other characters, but likely, they won't be a big deal. It's all about the main cast.
Wow, I said a lot. I am looking forward to the film. One thing that really got me thinking is whether Kishi is willing to have Sakura interact with Naruto's parents (if they are ALIVE). That will be awesome. Kishi, don't let us down.
P.S. Recent color chapters really tell me that Kishi clearly knows the main cast of his work. He's not going to be like "Let's have Naruto chill on the tree and have 'that' person calling his name". When he sets his work, it's set for life. Nothing will change his approach. We shall fear NOTHING!