If Izanami allows the user to change an illusion cast onto another to become a reality, so basically an instant kill (the illusion of that persons death), at the cost of blindness in one eye... (it is an IF, as we dont know yet, but it seems logical)
My point is that the 8th Gate, that actually kills the user, should be absolutely incredible in comparison. If you are blind and win the fight, its obviously better than dieing and winning. I just dont see it happening as Izanami and Izanagi seem way to over powered, and the prerequisit of Senju DNA (if true) seems far to easy to obtain atm.... the 7th Gate was also abit underwelming if you ask me....
I think Gai should have been killed off a while back, during the Kisame fight or something, and then brought back as an edo. He could have used the 8th Gate without dieing and been a ultimate badass.
I wish the whole story hadnt been so rushed, it could have been something really great, instead its just mearly kinda cool and something i still read because ive already put so much time into it.