Shunsui dramatically mentions squad zero as the royal secret service in pendulum chap -108 page 17.
People keep saying the vizards are going to come out and get involved in this fight, which seem very likely with the way events have been moving along. But its been over 100 years since any of them were shinigami. Though they were captains and vices they could be a bit rusty from sitting around in a warehouse and arguing all the time. I'm really curious to see how powerful the vizards are when they put their all into fights, especially hiyori.
if you recall back to the fight between ichigo and grimmjaw where ichigo first used his vizard power, hiyori handed grimmjow his ass and was about to kill him until the negation light saved him. im pretty sure the vizards are all very strong