I think he survived his fall down the shaft Vader threw him down in ROTJ, and using the dark side magic he learned from his own master (Plagueis), he survived, went into the Unknown Regions he was always exploring (he was obsessed especially at the end of ROTJ with that region of space) and is the puppeteer behind the entire ST. Snoke is his minion, either some mindless clone he's been manipulating from afar, or something else.
I think that this means that Kylo & his loyal Squadron of Stormtroopers will team up with Rey & Co. against the far greater threat of Darth Sidious/Palpatine & The KoR (I think in their absence they were co-opted by Palpatine directly). Aside from the Rey & Kylo scene from the beginning of the trailer (in which he doesn't fire on her), you also have the shot of Kylo slamming down what APPEARS to be a KoR in the forest (with stormtroopers on his side) showing that they've turned against him in some fashion. EDIT: Adding in that a big deal is made of Kylo getting his mask back, but in the shot from inside his interceptor (not in the trailer, but shown at the panel) and the forest scene it is conspicuously absent....and in the interceptor interior shot his face is cut up and bloody (which leads me to believe the turn happens in/before that forest scene)...so I think that the turn happens mid-film and Kylo and his stormtroopers (like Vader's fist?) are on the light side for the rest.
I also think this lends credence to the idea that Anakin will be present again in the finale. Perhaps Kylo, Rey, and physical manifestations of deceased Anakin, Luke, and possibly Obi-WAn (Qui-Gon too? Could they have gotten Liam back?) team up to take on the evilest badass in the galaxy, Palpatine and finally take him out for good.
Either way, the fact that Ian is 100% in the film and JJ and KK are so adamant that this was always part of their plan...this won't be a bit part, or holocron recording...I think Palpy is the Big Bad of the ST. It's not exactly DARK EMPIRE, so they're not really copying that....but if you are tying up the Skywalker Saga...how better to make it happen than to bring in a symmetry about the guy who effectively started the Skywalker family with his accidental creation of Anakin in the first place.
Also, I just learned that JJ went to the man himself, George Lucas (these were what the reports about Lucas being brought in to help were about), before he scripted the film...so one would wager it was in safer hands than it might have been from an "idea" level?
MakingStarWars SWEARS that the Lars Homestead features late in the movie...so I think that either Rey buries a deceased Kylo there, or it's where a post-redemption Ben Solo will spend exile after being responsible for so many deaths before turing back to the light.
This post has been edited by QuickTidal: 15 April 2019 - 03:35 PM