In HG/SS we got Groudon/Kyogre/Rqayquaza, so for the R/S Remakes we're getting Giratina/Dialga/Palkia would be my guess.
Sinister cloud in upper corner to me is Giratina or Darkrai represented, most likely Giratina. Space station, Palkia anyone?
Nothing on Dialga though....
Just located east of the kyogre design ocean area(appears to be a Regi style cave), but that's not where the Regi's are, possible 4th Cavern access for Regigigas?
Mauville for sure looks like its been transformed into a Power Plant facility. There are big walls as pictured in the wonderful artwork, but it defo looks like an actual building rather than plain walls.
North of Mauville looks like there's been a landlside of some sorts, just before reaching the desert. Looks like you might have to go up a cliff face, and then back down to reach the other side.
Devon Corp. looks small, if its even still there at all in Rustboro City.
I appear to see at least 2 small "lake" sized pools of water, with adjacent new cave locations that could possibly hold Mesprit/Uxie/Azelf:
1st is directly south of Sootopolis, big pool of water, with a walkable route with a cave entrance above it.
2nd is a little ways east of the 1st, big pool of water surrounded by mountainous terrain, with what appears to be access to a beach route.
Possible 3rd location could be up what appears to now be a double waterfall location above Fallarbor Town.
Where the Safari Zone used to be, i'm seeing a group of similarly shaded objects, but not the building itself, so possible location move to post-game, ala X/Y Friend Safari instead.
It's bad because it's shallow fanservice that takes a step back from superior gameplay just for the sake of being shallow fanservice. I've said it before, but if they're going to go that route, then they may as well get rid of the Repel prompt and multiple-use TMs.
How can the R/S remakes possibly be considered inferior to X/Y/Black/White solely because of 2 buildings in 1, that's beyond ridiculous. The Pokemarts are back because its a remake. It's called nostalgia, not fanservice.