I know that Piwi would have some importance around the end, and also that Shunova was a parent of Vermillion and would be too obvious if it was her mother.
In the end, it wasn't that big a surprise, problem is, EVERYTHING happened at once in this chapter and it's too convenient that Shunova came just in the right time knowing the details of everything that's happening with everyone.
This chapter was just a big: