Comprehensively long post incoming:
- Twinleaf Town, Sandgem Town, Lake Verity, Routes 201, 202: Mildly wooded area that leads to Lake Verity.
- Canalave City, Route 218: At most Canalave will be a small fishing locality. I don't expect their to be a harbor just yet. Might be accesable from Lake Verity northwards.
- Routes: 219, 220, 221: Wooded, coastal area leading to a sprawling scenery/valley (later known as PalPark).
- Jubilife City, Route 203, 204s: Small town on a plain, might be the starting town in this game, but I'm not sure.
- Everything between Eterna Forest and Route 204n: Barren wastelands from going from the coast to the rocky terrain of route 205s.
- Eterna Forest and Eterna City: Smaller town, but I could definitely see there being a settlement here. Eterna Forest would be lush, old chateau wouldn't be built yet.
- Oreburgh City and Route 206, 207: Maybe a little mining shack near the mines, but I don't expect a full city. Obviously no bikepath.
- Hearthome, Route 208, 209, 212n: A vast rolling field with a vastly smaller settlement in the middle as opposed to Hearthome City and Lost Tower would be a thing, but maybe more relic'y.
- Pastoria, Great Marsh, Route 212s: Just a big ol' marsh with a little Fortree-type settlement with some swamp-people praising Lord Quagsire.
- Solaceon Town, Solaceon Ruins: Basically a single farmer who talks about the 'ruins' and mysterious things, which would still be ruins here since I'm expecting them to pre-date Legends.
- Celestic Town, Route 210 and 215: Basically a wild area (not literally a Wild Area, but wilderness). Celestic Town would pretty much be the same with just older styled houses.
- Veilstone City, Route 214, Sendoff Spring: I could see there being a market town here, but vastly different then how we know it in modern Sinnoh. This would be a town before the meteors fell to the earth and blackened the soil. The route would obviously not have all those darn fences.
- Route 213, Valor Lake Front, Route 222: Just a coastal route without anything, definitely no hotel.
- Route 216, 217 and Acuity Lake Front: Snowy wilderness.
- Snowpoint City: I could see the temple being a thing and some ruins alongside it. The area would be re-populated later on in Sinnoh-history, because the area would be too cold to live in during the age of this game. Maybe some Inuit-like people live on its shoor where the harbor is now, but other then that I couldn't see it.
- SunyShore City: I'd expect seafaring folk to live there. So just some marooned ships? Obviously nothing highly sophisticated will be there yet.
- SpearPillar: I expect it to be intact.
Here's what I think.
- Definitely Celestic and Eterna will be out there since these are few of the oldest places in Sinnoh.
- Solaceon Ruins might be before it became a ruin.
- Oreburgh would probably be an old mining town.
- Pastoria was established to protect the Great Marsh and I see it on it's early stages.
- Canalave is probably just a small canal town.
- Snowpoint is a temple city.
- The three lakes should be there.
- Spear Pillar is not in ruins yet.
- Stark Mountain is a very active volcano.
- Other towns and cities haven't been established yet. But I expect new towns that aren't present in modern Sinnoh.
I'm expecting Veilstone to be vastly different as it feels too new in the current age. Kinda as if it was rebuilt entirely after those meteorites rained down on it. I don't know if the game will go to the PostGame-area.
Stark Mountain also isn't a part of the Sinnoh region yet. Not prominent on the Map, and it's why I don't think we'll see something like Iron Island or Canalave City (although it may play a large role in the story)
I find it interesting that pretty well 40% of the bottom-right of the Sinnoh region *should* be swampland but we haven't seen a lick of it. Same goes for snowy biomes- we've see light dusts of snow but no actual snow area. To tie back to above I also find it interesting that the main city isn't based out of Canalave- the city that is home to the Sinnoh Library with all the ancient texts. Libraries tend to be central to capitals and while this is a long branch to go out on, i'm theory hungry.
We've seen just one small bit of the game. I'm pretty sure we will see it be represented as swampland once we get closer to 2022 and get more information/perspective on the game.
I wonder if the settlement that's founded will eventually become Jubilife City. If this games set 100 years in the past in that time the settlement could turn into Sinnohs biggest city which happens to be Jubilife.
In my eyes, it should be Eterna City. But I could see it being Celestic Town, Jubilife or Hearthome as well. Maybe even Veilstone (before an apocalyptic event destroys it).