Many of us weren't surprised about the existence of a 3rd MS jutsu.
Susanoo is part of the same mythologies as Amaterasu and Tsukuyomi, so we pretty much knew the name ahead of time as well.

We also suspected that, since Amaterasu is ninjutsu, and Tsukuyomi is genjutsu, that Susanoo would be taijutsu...which....I suppose it sorta is...