It's possible. Gamefreak is not a small company. Odds are they set a team to work on this as soon as the dev kits for the 3DS went out. Even before Black and White (the first ones) came out. After the first fifth gen games were released the team working on it grew, and now they're all working on it.
So they've e been working on it for 3 years, give or take, if my guess is right. Could be anywhere between 100-150+.
Personally I'm hoping for 100. And I hope they stop adding new Pokemon soon. There is such a thing as overkill.