Might Guy is the only known ninja capable to utilize and open the Eight Gates and this is the perfect chance for Kishi to show it's true power. I believe it's the best opportunity to use it ( he almost did to save Kakashi against the Tailed Beast Ball ) to defeat Obito / Madara. It was noted that opening this gate gives the user power that is even beyond the five Kage, but comes at the expense of the user's death shortly after.
Beyond the five kage = something really powerful + BM Naruto + Eight Tails + Kakashi = R.I.P Madara.

Haha that's was quite crazy but I doubt Guy is going to sacrifice himself using this technique and actually fail to defeat someone.

I hope I didn't activate any trolling gates in some person's body.