I always think of ancient Greece when I imagine that country, ancient Rome would be ok to I guess. Maybe Italy would make an interesting basis for a region after all.
I think modern Greece actually has a lot to offer as base for a new region. Not only do you have all those nice ruins but also very varied terrain; you have sun-baked, desolate hills where nothing lives but a few hardy shrubs, you have river valleys with green forests, you have the north where it regularly snows every winter, you have massive mountains (like Mt. Olymp) beautiful seaside cliffs that the Switch could render very well... sunken portions to explore where you can discover ancient artefacts (and pokemon) large tracts of land that are used to grow olive, orange and lemon trees as well as grapes...
And there could be a lot of individuality between the cities, from busy, kinda dirty and smelly Athens (with it's cultural scene) to stunning little villages that are built into the side of cliffs...
Greece wouldn't be a bad Pokemon region. However unless they emphasize the barren nature of a lot of Greece's landscape then, as a subtropical place, and considering things are simplified and idealized in Pokemon games... Poke-Greece might end up a quite similar to Alola.... There's a lot of places in Greece where you could be fooled into thinking you are in the tropics with palm trees and white sand and everything.
Southern France (my big wish, since I'm not a fan that they left out the beautiful Provence, the most stunning place in continental Europe, imho, from X/Y) would have a similar problem, at least along the coast, it is more varied inland with the southern outskirts of the alps and all. And Southern France is quite different, culturally from Northern France...with much more Ancient Roman influence and ruins and all and more laid back as well.
And yes, I do want my friggin Unicorn. Rapidash just has a horn, it doesn't have any of the aspects of a Medieval Unicorn; it doesn't guard forests, it doesn't have healing properties, it isn't particularly "pure"(whatever that means) it's just wild. And I'm not sure even a regional variant could capture that completely, unless it's a very large difference in both Ponyta and Rapidash, like on the level of Alolan Exeguttor.
I'd really love a Fairy/Grass unicorn that learns Flower Shield, Healing Bell, Misty Terrain and Dazzling Gleam.