According to known Pokemon leaker Centro Leaks, the next Pokemon title will be set in Unova, the same location as Pokemon Black and White 1/2.
Centro Leaks posted an image of the Unova region captioned with "Next year's game hype has completely killed the DLC hype for me', along with another tweet that stated "2022: PLA (Past). 2022: SV (Present) 2024: ??? (Unova) (Future?)"
It's worth taking this with a pinch of salt, however, as Pokemon fans have been clamoring for a return to Unova for years now, with the region and generation a fan-favorite. This could be wishful thinking on Centro Leaks' part, though it is worth noting that they've accurately leaked several elements relating to Pokemon Scarlet & Pokemon Violet in the past, so they have a decent track record.
Pokemon Scarlet & Violet still has two separate upcoming DLC releases that both promise new and returning Pokemon, along with new challenges and battles for trainers to take part in.