Spoiler Naruto Chapter 611.

[DrKage]

But they could have cast the genjutsu in complete secrecy. I mean, maybe Kurama and Gyuuki would feel the rebirth of the Juubi but if they weren't anywhere nearby, who's to say that Obito or Madara couldnt have revived the Juubi, sealed it, summoned the moon (whatever that means), and cast the jutsu in a shorter time than it would take Naruto or Bee to get there?

I like the recollection that the tailed beast could snap the jinchurriki out of a genjutsu and that makes it more likely that's the reason they were collecting them. If Obito cast the jutsu, would he have to maintain it? Would Madara? And then could they fight off jinchurriki who would show up to stop the genjutsu or snap other people out of the genjutsu?