Three possibilities:
1. These two games are the "Pokemon Z" we have all been waiting for. Note in gen 5 we waited for "Pokemon Gray" but instead got two new games, sequels to Black and White. (Point conceded that they shared the same naming scheme as BW.) The Zygarde arc is still completely untouched and it doesn't make sense for it to be restricted solely to the anime, never mind Volcanion who we all just met a short time ago. With that said, "M" and "S" seem to be completely unrelated to Zygarde, Volcanion, or Kalos in general, which leads me to believe...
2. "Z" is still the sequel to X and Y we've been waiting for, and "M" and "S" are unrelated, separate titles. I'm not really keen on this because if there were three trademarks filed, they would have been found. (Has Pokemon Z been trademarked? Gamefreak has trademarked titles they never use.) I would be more inclined to subscribe to this theory if it weren't for one Pokemon: Magearna. We (collectively, the world) were introduced to Magearna at roughly the same time, and if X and Y are any indication, that means...
3. "M" and "S" are the flagship seventh generation games. The naming scheme is completely different, as is the norm for a new generation. The logo is also very different from X or Y, which resembled Xerneas and Yveltal respectively. X and Y were both announced through a Nintendo Direct, and were revealed to be being released worldwide at the same time - a first for the series. Note how English reveals for Diancie, Hoopa, and Volcanion were all done almost in tandem with the Japanese release? This is the new standard. Magearna's reveal, followed by a Nintendo Direct, leads me to think that Magearna is going to be hailed as the first Pokemon of the new generation, to be caught in the new games.
While Magearna and Volcanion are appearing in a movie together, it doesn't mean they have to be from the same generation. Pokemon has teased future-gen Pokemon in the current gen.
X and Y were also revealed around this time, three years ago (January 8), and they were released October 12 of the same year.
I have a feeling that when the direct happens, we will see the flagship legendary Pokemon of these games, as well as a November 2016 to February 2017 release date.
You heard it here first.