Though things look as concrete as they are (with said 4 idols being unproduceable and all), I'm still to wait for that TGS event. A lot could go wrong if speculation went around so fast, people might mistake it for the truth. After all, there are a lot of people who love them, so I believe namco would make a pretty bad move not to even put them as unlockables.
Anyway, Ritsuko and her idols, huh? Basing with what we know so far, Ritsuko is probably a producer for 765 and hence, your in-company rival (Oh God, the ideas coming out of that). Making further speculations with what could happen........*silence, then stares at 961 with determined eyes*