actually, i would say the most likely one to open the 8th gate is lee. i don't think there's much of a diffrence between the gates on the way of opening them, it's like the diffrence between lifting 10kg and 50kg, it's the same technique just much harder...

i can easly imagine him knownigly sacrefising his life to protect his improtent person, he seems to have a knack to big flashy sayings...

besides, we don't know if Gai is even able to open the 8 gates, the comment kakashi made about Lee being a genious after all can stand for the fact lee can open more gates than Gai...