I had a thought...
I noticed naruto started to hyperventilate when sasuke activated susanoo for the first time. It's a farfetched theory but maybe itachi's gift was some way to bond naruto to sasuke. if this is the case, then by next chapter naruto should be writhing in pain from sasuke awakening the perfected susanoo.
maybe at some point sasuke will notice it causes naruto harm, and will try to reduce the amount of times he uses susanoo, which it turn will stop his descent into the darkness. but i doubt, since itachi was a genius and all, he wouldn't give sasuke a gift that would merely stall instead of improve.
And I think izanagi is some form of life-system jutsu. think of it as a cat. they say cats have 9 lives. I noticed everytime danzou ought to die, an eye closes but does not reopen, so we know its not a jutsu that has a cooldown or requires charging up.
I vaguely recall a scene where madara says something like "I need to collect more eyes". And seeing his reaction, madara was probably aware of the existence of such a jutsu, quite possibly knowing it himself. And i assume everytime you would die, an eye is sacrificed instead of one's own.
See initially, danzou was forced to use up his eyes because he had no idea what sasuke was capable of. one might view it as sasuke being imprudent and using up his best techs from the beginning, but unknowingly forcing his opponent to use his strongest as well.
that being said, danzou was forced to use up some "revival eyes". thats precisely why he dodged the arrow with his shoulder-grow-tree no-jutsu and kicked karin; he needs to conserve his chakra and lives.
i mean, we've seen many characters having some form or another of immortality; kakuzu, hidan, juugo, sasori, obviously madara, pain (well, not immortal per se but he can bring dead people back to life, which is cool in itself, like orochimaru +2 summoned hokages vs sarutobi).
NOTE: i mentionned juugo because we have no knowledge of how old he was when he was detained by orochimaru, but when he gave part of his life to sasuke after having his chest blown open by killer bee, juugo kinda gave his years of accumulated youth to sasuke in order to regenerate him. as such, juugo simply turned back into a kid. id say thats one badass ability if you can find yourself a badass partner, immortal duo.
Theres foreshadowing about danzou's knowledge of izanagi when he tells sasuke he's as far below itachi as the ground is the sky, izanagi being one of the 3 gods born from nothing and god of the sky. for sure theres a 5th tech or variation of the 4th MS tech, being Izanami, or maybe izanami is the mugen tsukiyomi madara was talking about.
What I can't wrap my head around is the panel where danzou says "release". it's probably something to do with his izanagi tech but I don't know.