Officially unconfirmed, but you're surprised?
THE iDOLM@STER, a pop star management simulator, was originally released in Japanese arcades back in 2005. The inevitable Xbox 360 console port was followed with endless DLC as well as spin-off titles on the PSP, Nintendo DS and a mecha anime created by Sunrise, the studio responsible for Gundam.
The per-console-Xbox-LIVE-sign-up-rate is so high in Japan because of this game and this game alone.
What is rumored to be a leaked release from Microsoft Taiwan shows THE iDOLMASTER 2 penciled in for February 2011. What is suspicious is that there has already been a sequel, THE iDOLM@STER: Live For You, that was released back in February 2008. It is not THE iDOLM@STER 2 per se, but it was a sequel.
What gives this rumor precedence is how THE iDOLM@STER has been merchandised out in the past as well as vague rumblings on iDOLM@STER development team blogs stating alluding to beginning work on "the next work". What's more, a February 2010 entry in the staff blog even makes reference to "this time next year" is when it seems like we might want learn what the idols have been up to, but then more can't be written without ticking off the bosses at game develop Namco Bandai.
They've already put this game on a credit card. What's stopping them from making more iDOLM@STER games?
Xbox360 『アイドルマスター２』 ２０１１年２月発売！！！ [オレ的ゲーム速報＠刃]