We broke the news about it just yesterday, and we were indeed right: the count down site opened by Steins;Gate developer 5pb. a couple days ago was indeed for an Infinite Stratos game, and more precisely for Infinite Stratos 2: Ignition Hearts.
The official website was opened today and revealed the game as a PlayStation exclusive (for PS3 and PS Vita) adventure visual novel to be released this winter in Japan, based on the second season of the Anime series that will air this fall.
Looks like 5pb. is moving quite solidly to PlayStation exclusivity from developing a lot for Xbox 360. They have announced quite a few games for PS3 and PS vita lately, including Rozen Maiden: Wechseln Sie Welt Ab just yesterday. We can only hope to start seeing some localization of their games as well, sooner or later.