Considering that Deoxy was promoted (demoted?) to being obtainable in the Delta Episode in ORAS, I would not be surprised if Volcanion became obtainable through normal means in this gen. For one thing it hasn't been released yet, so it's nature might turn out to be different than expected.
More importantly however, the current running theory for the games setting is that it takes place in an expy of either Spain or southern France. In the event that the game's setting does turn out to be Southern Kalos, which was cut off from from Northern Kalos in XY by a barrier of mountains, then its not unlikely that Volcanion will be important to the lore in some way, as what we do know of it lorewise is dialogue in the games mentioning that it created the plains of southern Kalos via a massive steam explosion, and it is revered by southern Kalosians for it.
Not only that, but in the upcoming movie featuring Volcanion and Magearna features a location called the Azoth Kingdom. Normally it would seem to be just one of the random wacky locations/villain factions that tend to appear in the movies. However this time it's a bit more significant due to the fact that in ORAS the Magma and Aqua plots were codenamed project AZOTH, which in its documents that were readable in the game made specific reference to Kalos due to the relationship between Mega Evolution and Primal Reversion, and tied back to the ongoing backstory lore plot regarding the Infinity Energy. Moreover, the grunt who references the project expresses confusion over its name, only knowing that the first two letters were representative of the beginning and end, and is left wondering what the rest of the name is for.