Summary
While manyPokemonfans were expecting to see a new game set in the Unova or Johto Region announced during the Pokemon Day festivities,Pokemon Legends: Z-Ataking players back to Kalos was likely not on many fans' bingo cards. The Kalos Region was the setting for Gen 6’sPokemon X and Y, which many players felt was incomplete due to the lack of a third, definitive version.Pokemon Legends: Z-Amight fill the gap left by this missingPokemon Zversion, but the game may not actually be set in the Kalos Region that players are familiar with.
It’s unclear just how much players will be able to explore the Kalos Region as a whole inPokemon Legends: Z-Aas the game isset entirely within Lumiose City. This setting is a stark contrast toPokemon Legends: Arceuswhich featured multiple zones around the region that players could openly explore. However, these two games' settings might share one commonality ifPokemon Legends: Z-Ais set in the past, as it’s likely that the Kalos Region might be called something completely different in this title.

Pokemon Legends: Z-A May Have a Different Name for the Kalos Region
InPokemon Legends: Arceus, players travel back in time to a past version of the Sinnoh Region, home to the Gen 4Pokemongames. However, rather than being called “Sinnoh,” theregion is referred to as Hisui, since that was the name given to the land by the people who inhabited it during that period. While the Sinnoh Region and the Hisui Region are technically the same land mass, giving the region two different names helps distinguish Gen 4’sPokemon Diamond, Pearl, and Platinumfrom the very different game that isPokemon Legends: Arceus.
Another reason for this name disparity is likely tied to the real-world Japanese region of Hokkaido, which theSinnoh Regionis based on. Prior to the Meiji Restoration in 1869, Hokkaido was known by its inhabitants as Ezo, so the Sinnoh Region being known by a different name in the past fits with the history of its real-world inspiration. France, the real-world inspiration for the Kalos Region, has also had a different name in the past, as it was referred to as Gaul by the Romans, but it’s unlikely thatPokemon Legends: Z-Awill be set far enough in the past that it will need to mirror this name change.
Why it Makes Sense for Pokemon Legends: Z-A to Distance Itself from ‘Kalos’
Although it might not make historical sense for theKalos Regionto have a different name during the time thatPokemon Legends: Z-Ais set in, there is still a good chance its setting ends up being called something other than Kalos. Since havingPokemon Legends: Arceus' setting named Hisui has helped distinguish it from the setting ofPokemon Diamond, Pearl, and Platinum, it’s likelyPokemon Legends: Z-Awill do the same to distinguish itself fromPokemon X and Y. This will be especially helpful if the game introduces new regional variants, as referring to a mon by its Kalosian form might get confusing since it’s not available inPokemon X and Y.
The most simple solution forPokemon Legends: Z-Awill be to simply refer to its setting as Lumiose since the game is said to take place entirely within Lumiose City. This way, new regional variants could be called Lumiosian variants and would be distinct enough that fans could distinguish between theKalos Region ofPokemon X and Yand the version present inPokemon Legends: Z-A. Even if players can travel to areas around the outskirts of Lumiose City inPokemon Legends: Z-A, this naming convention would still be appropriate and would be able to encompass the full scope of the game.