Tobi is Madara
Madara was "killed" during his battle with the 1st Hokage
Tobi states he is only a shell of his former self.
Sasuke stated susano'o is only possible to those who wield DOUBLE mangekyou (Amaterasu AND Tsukyomi)
Danzou is escaping deaths and his sharingans close.
All this leads me to suspect that Madara sacrificed one of his eyes to return to life, and as he has done so, he can no longer wield Susano'o anymore, but there are ways to reactivate them maybe, and thats what he appears to be doing.
Madara was "killed" during his battle with the 1st Hokage
Tobi states he is only a shell of his former self.
Sasuke stated susano'o is only possible to those who wield DOUBLE mangekyou (Amaterasu AND Tsukyomi)
Danzou is escaping deaths and his sharingans close.
All this leads me to suspect that Madara sacrificed one of his eyes to return to life, and as he has done so, he can no longer wield Susano'o anymore, but there are ways to reactivate them maybe, and thats what he appears to be doing.