First of all, what will it be about from what we can see here? From the first shot, we can already tell that Rey will go through her training with Luke on Ahch-To in order to go up against the First Order. She apparently struggles, gasping for air as if she had a disturbing vision. We hear her theme music on top of (possibly) Luke saying, "Breathe. Just breathe." It seems right away like Episode VIII will give us what we're expecting from it: Luke training Rey to raise up the next generation of Jedi knights. In fact, it seems that quite a lot of time will linger on her struggles with Luke on Ahch-To, similar to when Luke was on Dagobah with Yoda.
Then we see what is presumably the Republic looking at a map, following a *gasp* cracked version of Kylo Ren's mask.
Okay, now this raises lots of questions. What happened here? Did Kylo just fall on his face or something? A tragic event must have happened between Episodes VII and VIII to cause a downfall in his reputation or capacity to rule the Knights of Ren. Maybe it was his defeat against Rey, maybe it was the destruction of Starkiller Base, but either way, he will be much more wounded than the last movie.
Then there's another unfamiliar image new to the Star Wars universe: some sort of platform surrounded by wood, and a closeup shot of some ancient book. What on earth could this be? Maybe this provides some backstory to Rey? Maybe this is where Supreme Leader Snoke keeps his base? No answers given yet, but I am guessing this new location is tied in some way to Snoke.
Then these ships charge against an army of AT-AT Walkers(?) with Finn in one of the seats, eyes closed. Is he maybe relying on the force to fly his ship? If he is, then he clearly didn't listen to Han.
Anyways, Po and BB-8 are running inside some base as it is destroyed. Then there's *bigger gasp* the millenium falcon! What? I thought that Han Solo is gone? Who else is there to fly it besides Rey? Isn't she in some other part of the galaxy? If you ask me, it could mean that the First Order got a handle on the map to Luke Skywalker, and sent the Knights of Ren to Ahch-To in an assassination mission against the Last Jedi?
I should say that this is what we're in for, as another one of the poignant images in this trailer is the Jedi Temple in flames, Luke and R2-D2 watching in dismay. We also see that Captain Phasma and her squad set the flame ablaze, so this could also mean that we'll get more Phasma than we were promised in The Force Awakens.
So the last thing that we see and hear is Luke Skywalker in the shadows with a voice declaring, "It's time for the Jedi... to end."
Is this really true? Will this movie actually see the end of the Jedi? Will the First Order accomplish their mission? Will Kylo Ren really redeem himself? Will Luke and Leia reunite as brother and sister? Will Leia have to face the death of yet another relative to the First Order? Will we learn who Rey is actually related to? Is she the Last Jedi we keep hearing about? Who IS Supreme Leader Snoke? Where the heck is Chewbacca? Is Jar Jar Binks still alive?
Star Wars Episode VIII: The Last Jedi will mostly focus on Rey's Jedi training with Luke. Although Skywalker has already lost hope after seeing how much of the galaxy the First Order has conquered with Kylo Ren's leadership. But he sees that Rey is already strong with the force, so he decides to give her a chance by training her. It is through these training sessions we learn about Rey's backstory, including who she is and how she ended up on Jakku.
But back with the Resistance, they are in deep conflict against the First Order, as Kylo Ren has already sensed that they know Luke's location, and he sends his knights to locate the Resistance in order to obtain the map. Finn feels the need to go and warn Rey, but General Leia tells him it's too dangerous to leave the base. Yet he still won't quit, so he volunteers himself as a pilot against the First Order's attacks, with his friend/mentor Po by his side. After a successful battle, Finn proposes again to General Leia to leave and warn Rey. Leia says there's no use: Luke has already sensed it, so it's up to him whether he should leave the Jedi Temple to protect himself.
Although it's not Luke Finn's worried about, Rey doesn't know yet. So he and Po set off in a ship unsupervised, and light-speed their way to Ahch-To.
He does manage to reach Luke and Rey, but all this reunion does is cause more guilt within Luke for letting his brother-in-law get killed. It also turns out that Finn and Po's ship was being tracked by Captain Phasma, leading into a battle that ends with the destruction of the Jedi Temple. At this point Luke is convinced that the First Order has won and there's no hope left in stopping them, seeing there's only one Jedi left in the galaxy. He says this just as he collapses and dies of a broken heart.
Now it seems that the First Order has succeeded in their mission to fling the Jedi into extinction, until Kylo Ren speaks up to Phasma about Rey's knowledge in the force. Now the First Order has a new target on their hands.
There is no way anymore that Rey can return to the Resistance, she's too easily spotted there. She needs to go out across the galaxy with her three friends, including BB-8 and R2-D2, the last left of Luke Skywalker, and search for anyone else out there who could have the force. Maybe the Jedi's not dead after all...
But that's just my prediction as to what this movie will be about. We may not know who Rey is really related to, it may just as well be saved until Episode IX, which thankfully leaves room for plenty of other epicness. We'll just have to wait and see this December, which sadly cannot come soon enough!