i am curious as to what gives you a feeling that Kalos is incomplete?
Off the top of my head, at least:
- Couriway Town having a railway station with tracks going off in both directions, seemingly to nowhere from nowhere.
- The Ghost Girl in Lumiose City (and the identically-modeled girl in Hotel Richissime who mumbles something about "hearing the elevator", plus that building where only floors 1,2 and 4 can be accessed - there's clearly an elevator-related mystery left to solve).
- Kalos Power Plant having several doors but only one which can be opened.
- The Chamber of Emptiness being all empty (then again, what would one expect...).
- One of Kalos' only
three in-game legendaries having several alternate formes that were not addressed in the Kalos games.
- Big Empty Buildings: Kalos Edition: The Tower of Mastery, Prism Tower, Dendemille Windmill, Shabboneau Castle, Ambrette Aquarium... the region is littered with landmarks with exactly zero purpose (the Lumiose City Gym could have been in any building whatsoever, whereas Prism Tower would provide a lookout point over the entire region - talk about wasted effort to
not have any windows whatsoever in the Gym).
- "I'm going to go for help. Wait in the usual place" - mysterious message hidden in Lumiose Station.
- Rivers criss-crossing the entire region, connecting several cities and even intersecting Lumiose City, but exactly none of them are ever used for any transport. They're even on the Town Map, showing that they're quite deliberately connecting the settlements of Kalos, but have no use whatsoever.
- Cyllage City's racing track.
- Thousand Arrows/Thousand Waves.
- AZ's Floette being coded into the game, but not released. The move Light of Ruin shares this predicament, as it is Floette-E's signature move.
- That Rhyhorn Racing track visible (but inaccessible) from Route 22.
- The last one is a bit of a stretch, but I believe it has enough validity to warrant further attention:
There's a big mountain in the center of Kalos. The middle of the region is just empty space, with two quite prominent natural features dead center in the map.
It looks even more prominent on the Town Map. A big mountain south of a big forest, on a line straight south from Lumiose City. The river connecting Santalune City and Camphrier Town goes right between the two. That location feels way too prominent not to have any features in the game. It could have been a beta location for the Pokémon League, though, moved to its current location to better suit the theme of coming back where it all started after beating the eighth gym.
At a stretch, I'd even put "Coumarine City having a monorail for no good reason" in there too, though that could have been the developers' effort not to have to code a cliffside town, or a progression obstacle that was dummied out (Face it, half of us were expected to be greeted with "The monorail is currently broken" when we entered that building).
Anyway, the conclusion is clear: Kalos promised a lot more than it did deliver on. Now, I don't know how many of those were ever planned to be elaborated on, or what was cut from the game during development. But fact remains that there's a whole lot of loose ends all over Kalos, which could have been explored very well in a sequel game.