User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-26285797-20150506120633/@comment-26209278-20150506124743

Because Vali isn't strong enough already with another upgrade....

Jokes aside, it'll be interesting to see what happens. It may be more interesting to see if he unlocks something else, instead of unlocking something Issei already accidently unlocked as well.