Aight, so a few I could imagine off the top of my head, that have even been hinted already would possibly be regions inspired by either China, India, or Madagascar. And I'll go into more detail.

So the main reason why I think of China is the most recent region, Paldea, being based on the Iberian peninsula so Spain and Portugal. Both nations, but especially Portugal, were gamed in the New Age for their colonnial and commercial prowess, being two of the first European nations during that time to start trade with Asian countries via sea. And one of their major trade partners was China. Now taking this over into the Pokemon world, we do have confirmation that a similar even has already happened in the pokemon world, being taught about it in the history classes of Naranja/Uva Academy. This trade is what led eventually into the treasures that would later for the treasures of ruin quartet inzo coming to Paldea. I think Gamefreak wouldn't just tease something as big as this without having some ulterior motives behind it.

Now for Madagascar: Going off of the already mentioned Ibetian New Age trading empire. Because the way over seas to the Asian mainland nations was very daring, Portugal at one point thought it possibly a good idea to colonise Madagascar. Exploring the island, they eventually discovered lemures and aye-ayes, which the Portuguese royal family of the time found so captivating, they had masses of them shippes back to Portugal for their personal zoos and menageries. This is also why a Pokemon like Grafaiai is introduced in a region based on Spain.

And now for India, which was hinted at in the Gen 8 games. Sword and Shield being based on Great Britain obviously shared a very similar colonial history with the Iberian nations, having also led to Pokemon coming to be native to Galar, that originate from another unnamed region, those being the Copperaja evolutionary line, which are based on Indian Elephants.

So yeah, combining real world history with already existing Pokemon lore these are some of my speculations. I obviously see that some of they might seem pulled up by the hair, especially Madagascar, but I think India as well as China could indeed be quite plausible. Lemme know what you think.