^Nope. Shaymin was released before Platinum... in Japan. That's the problem with english sets. They hold on some cards to make it tie with the newest game or whatever, but DP7 was a movie-themed set and supposed to introduce Shaymin, so Shaymin was in fact made into card before its new forme made its game debut.
They're not teasing anything IMO. We all know Zygarde is gonna be the next mascot, they're gonna have something new for it and as much as I'd like the game (yeah, just one) to be called Z, now they decided to start breaking patterns, so we have no ideia if we're going to have just one game, or another pair, like Gen V.
Nonetheless, the thing is now they're focused on Hoopa and the movie, they're still riding ORAS wave and I don't think we're going to see the next Kalos games until 2016, precisely because they're not showing any interest in teasing Zygarde. Also, if Zygarde will have new formes, they're probably going to use them for the next movie, so another reason to not expect anything Kalos related until mid-next year...
I do admit though, no Zygarde card yet is strange but at the same time, it seems to me that with each gen, they increase the mystery surrounding the 3rd mascot...