it's nicely thought of, the midnight dragon technique of Guy in 8the gate mode.
it's actually plausible, there are some other hints that might fit in there.
Guy is in that battle with kakashi and naruto, right now naruto freed the tailed beasts from their bonds to the jinchuriki and their chakra has been stored in the Gedo Mazo statue. naruto seems to have worked up his time in the biju transformation mode also but he still has to defeat the Gedo Mazo statue to free the tailed beasts completely.
With the recent chapter itachi has been talking about recognizing what you can and what you can't do and relying on your friends to fill in for the things you can't do. that this makes you perfect, and he had a memory of naruto at that time.
so here is what I think will happen in light of this information combined with your proposed technique of the midnight dragon.
both naruto and kakashi will not be able to destroy the gedo mazo, but Guy has his 8th gate and that was said to be legendary, he even thought he could blast away 5 biju bombs with it. Even though naruto does not want his friends to sacrifice themselves for his sake but I think guy will be able to convice him this time. knowing that this will put a serious dent in tobi's batle power and free all the beasts. and if tsunade or sakura can get there in time they might be able to save his life.