It's almost February, still no game-reveal despite the big Zygarde-Marketing having started half a year ago and meanwhile being sort of overshadowed by 20th-anniversary nostalgia milking.
This post is basically going to be random details about what X&Y-sequels would feature if Gamefreak wanted me to oversee the development. Just for fun.
Although I'll try to keep it realistic/plausible (no "all regions"-nonsense etc.), NONE of this should be taken as a serious prediction. It's more what I'd want it to be, rather than what I actually expect it will be.
I'll start with a symbol:
In my hypothetical X&Y-sequels, this is the new Kalos Symbol. Replacing the Pentagon.
The region of Kalos gets several new places, with the initial group of them located in the implied "southern"-part of the region (which is of course where the new starting town is).
As before, the Coastal and Mountain-parts are still where they were, west and east, while the previously Central part of the region is now the North, as the center of the expanded map shifted south of Lumiose City.
The colors neatly fit the mascots, blue and red for Xerneas/Yveltal, the new part being green like Zygarde, with the capital staying a neutral white (while also representing an unexpected "white" mascot of XY).
Now that the region is made up of 4 equivalent parts, they can perfectly function as fixed "season"-areas. Starting in the fresh new southern part with a Spring-aesthetic, going into the summer-feel of the coast, then the autumn-like places of the north, and finally the wintery mountains in the east.
The Kalosdex shifts around a bit, but overall expands from 3x150=450, to a 4x150=600, with the new green-part having a vague theme of spring (lots of field, grass, river pokemon), adding things like Rattata, Wurmple, Pidove, Deerling, Growlithe, Finneon, Clefairy...
Main-gameThere would be difficulty options available from the start this time (also known as Easy and Challenge mode in BW2).
The story of course takes off a few years after the events of X&Y, with new protagonists, also being given the Kalos starters (but this time, instead of being overshadowed by Mega-Kanto-starters a few towns into the game, they stay in the spotlight with their own new mega evolutions).
The order of the gyms is changed a bit, with some being replaced completely by new ones. Same with the E4.
Some previous places are expanded (Power Plants), get some relevant function (Pokeball Factory selling Pokeballs including HGSS-exclusive ones), or serve as a path to a new location behind it (Parfum palace/Glittering cave/Azure Bay...).
Completely new locations include a Rhyhorn racing track (with mini-game), a volcanic-dungeon, a more cheerful/magical forest (meanwhile Santalune forest being taken out altogether), a smaller but stunning diving-area etc.
The mascot of the Z-version is obviously Perfect Zygarde. While the mascot for the XY-version is a completely new, creature-design, most prominently white, with red and blue details. It is a, by all means legendary, new higher form of AZs Eternal Floette.
Zygarde and AZs Floette, are relevant throughout the game respectively. Both involving a quest to collect 5 colours of smaller creatures (5 Zygarde Cores with a differently coloured hexagon-core, and 5 special Flabébés with differently coloured flowers). At the same time the villains are capturing the ones from the opposite version mascot.
Post-gameBesides the starters, other Pokemon also get in on this third wave of Mega evolutions. Including Raichu, Clefable, Golem, Blissey, Milotic, Luxray, Goodra...
Legendaries that can be encountered include:
-legendary birds (all 3 in fixed locations: Frost Cavern/Power Plant/a new volcano location)
-1 of Lugia/Ho-oh
-1 of Dialga/Palkia
-1 of Tornadus/Thundurus
-1 of Reshiram/Zekrom
-1 of Xerneas/Yveltal
(basically all the legends that are harder to get in this generation due to them being version exclusives)
The Battle Frontier project is completed and replaces the Battle Maison, with the following facilities placed in a hexagonal pattern:
-Battle Tower (Battle Maison with a new look)
Move-Tutors from ORAS are all in there as well, with a fifth one added (Sucker Punch, Defog, and some new additions, including Toxic Spikes, Wide Guard, Ion Deluge etc..)
And there is a Battleground, where daily re-matches against Gym Leaders and other important characters can be done. With everyone having a Mega on their final team.
Trainer customization returns with a vastly expanded wardrobe.
As does the DexNav from ORAS
At some point you get a Mysterious egg, which can hatch into one of all existing baby-Pokemon randomly, with a very high shiny-chance (similar to the special egg in Crystal).
I think that would be the closest to a perfect game that the final instalments of this generation could be.