Other than what we already know which is he can't be edo and control the juubi

Perhaps there is a point of chakra overload?

In chapter 591

Madara states that there is one risk to the jutsu
That as long as you know the seal you can release
Edo tensies summoning contract and that there is
Nothing more troublesome than doing that...an undying body..unlimited chakra..it cannot be controlled

Then he goes rampage asking who summoned the contract

Why would the mighty madara be frustrated at the point that he has unlimited chakra? And why did he go after naruto as soon as he released the seal?

I believe its because he has limited time before the big kaboom. Let's be serious..there is no1 that can defeat madara. Not even naruto and sasuke...not even the shinobi alliance...

Perhaps the real reason he can't become the juubis host in edo form is because he will have a chakra overload and explode. Maybe the chakra is unlimited but the bodys resistance remains the same. Which is why he's been more of relaxing against naruto and bee and kakashi and guy. Not rushing the process

Like itachi said every jutsu has a weakness. I believe even if you release the contact there is still a downfall

This is simply a theory I've thought of doesn't mean I'm saying its going to happen.