Naruto Chapter 609 Speculation - Will 8th Gate be used.

[TurrinB]

What is Guy going to do with the 8th gate? Take down Madara? LOL No.
Take down Obito? That's Kakashi's job.

Hold off Madara for a bit so Naruto and Kakashi can focus on taking down Obito

Of course that would be a possibility, but as I said, Kakashi wouldn't let him use it, and if Naruto knows the effects of it, he wont let him either. Only possibility is - as I said - if they have no other option. As for now Gai can be pretty useful with just 7 gates, since Naruto is so imba. But whether he an handle Perfect Susanoo or not, is hard to tell, since we didn't see that much of it. I doubt it though.. But Naruto also got something from the other bijus.

Well Gai could just do it without their permission.