im on it
the first island is mostly canyons with grassy areas surrounding it. there is a large tree in the back that will likely play some significant role in the story. to the right there is a dark area with some kind of geyser or trail of light shooting upwards. my guess is that this is the area where you find Lunala, but i cant say for sure. What i can say for sure is that at the highest point on the island we see a pillar with a small platform at the base and a ramp leading up to it. this is likely where Solgaleo will be found in game.
the second island might be hard to tell at first glance, but turn it, and you can see that its the starting island from the trailer. we already saw a lot of it more in-depth in the trailers, so i wont spend too much time here but the placement has me thinking-- you will likely travel through the 3 main islands being the second, third, and fourth, in that order, and then go to the first when you are ready to fight the legendary.
the third island features a possible 3 or 4 towns with other areas to spare. also, if you notice, it is actually 2 separate island connected by a small bridge. this island seems to feature volcanoes, some form of water-related structure, and a manor, or estate as some games have featured before it. my guess is that you will start at the southern most tip and move your way upwards to the water area. then you will head back down south through the volcano area and manor until you reach the beach to go to the last island.
the last island is by far, the largest. from a glance it appears to have only 2 cities but a ton of other areas where people may appear. you can see ruins at the northern side, going south there is some form of spring, an oceanic area which means you will likely not get Surf until this island, what looks like a haunted house, then headed north im not sure what that area is. in the center of the island is a mountain which looks like a city is located on top of it. and just to the north of that is what i believe to be the Pokemon League castle.
there are also smaller islands surrounding the area. one is obvious, being right next to the first island, and another is hidden by clouds in the top right of the image. i think this is hinting at mirage islands returning from ORAS, but they could just be small details.
next, throughout the ocean, you see ships traveling between the 4 main islands suggesting you will use them to reach new islands and not use Surf, as some people have been theorizing.
in the center there is a huge white building floating in the water that i believe to be this game's post-game area, being either a battle frontier, battle resort, or something else entirely.
there are other details worth point out though, the islands are in a crescent pattern leaving a huge portion of the image just open water. it may play some significance, or it could just be there for show. also, the though of islands makes me wonder if the towns and cities wont have a linear order at all. maybe you could visit them in whatever order you choose, but it is unlikely.