Forgive me for asking, but where's the proof that only 9 Idols will be producable in Idolm@ster 2? If that's so, the 2nd PV is very misleading.
I believe it was straight out of Sakagami's mouth during the TGS event. Otherwise, this very ominous sounding comment from Ishihara, during his interview with Famitsu (linked earlier).
EDIT: I'd like to add that, my memory could be a bit fuzzy whether he actually said, word-for-word, you couldn't produce them, but I remember hearing something out of his mouth that pretty much confirmed it for me. I'll never forget that feeling...
ユーザーの皆さんには春香のプロデューサー、千早のプロデューサーではなく、765プロのプロデューサーになって、自分たちといっしょに彼女たちを盛り上げていってほしいということなので。
I would like everyone to not think of themselves as Haruka's Producer, or Chihaya's Producer, but rather as a 765 Producer, and enjoy their time with the idols in the game that way.
The Im@s2 main page says you can add two guests to your unit for a stage live, from Ryuuguu or from the 6 you're not producing. This was also reported in Famitsu.