The Bijuu's are stupid if they join the fight now, Madara would seriously do what I've speculated in my latest thread which is gather all the Bijuu and become the Juubi's host.
I honestly don't think Madara is going to get the Bijuu. I think the God Tree is going to bloom and Madara is going to obtain its fruit. It's been over 1000 years since the last fruit blossomed.
The tailed beasts are going to fufill the Rikudo Sennin's prophecy and reunite( give a large portion or all of their chakra) to Naruto and he will be the new Sage of 6 Paths. The Infinate Tsukuyomi is probably about to go off hense that haze that is filling the field. and only a few (Naruto and Sasuke) will break free or resist it.
Ultimately, I think this is going to be a 2 VS 1 fight. Naruto and Sasuke VS Madara. everyone else will be under infinate Tsukuyomi.