So, we've got the map of redesigned Hoenn now. Despite its tiny size, we can see some things if we look closely.

-PokeCenter and PokeMarts are separate. There doesn't seem to be any boutiques or anything like this added.
-We're back to the dull uniform Gym design. They are all yellow buildings.
-Looks like Slateport, Vendanturf and Fallarbor Cities have Contest Halls (since it looks like Slateport has the same building). I guess this was predictable, since Contests are Hoenn's "big feature" and they'll probably be heavily hyped during the game coverage, while the Battle Tents were a gimmick.
-The Route near Meteor Falls has been made more meteor-like now, with craters and all that stuff. Except Forme-changing rocks for Deoxys there (and possible Magneton/Nosepass evolution spot).
-Mauville City seems to be the most redesigned city. Looks like it's surrounded by a wall (with gates, unfortunately).
-Hard to tell if Altering Cave is accessible (I hope it is, since I'd like them to finally give it a purpose).
-Trainer Hill seems to be gone (it was originally an e-Reader thing, so I guess they preferred to axe it, rather than giving it a new purpose).
-The small beacon on the Lilycove Seaside seems to be bigger. Maybe it'll be given a purpose?
-There seem to be no notable additions in the continental part of Hoenn. However, the marine part is heavily redesigned, with many new islands and islets to explore.
-EverGrande City seems to be added some new buildings in the pre-Victory Road part. Perhaps it'll finally feel like a city?
-It's hard to locate Sky Pillar? Maybe it's under the cloud between Sootopolis and Pacifildog?
-The Battle Tower/Frontier (hopefully the latter) is likely covered with clouds.
-Southern Island is safe and sound, in case you had any doubt about its returning.
-And yes... There's that black blob on the north. But you've surely noticed that.