From my usual sources (see the sidebar to the right. Not only do I make regular use of them, I want my readers to as well), my guesswork proves to be correct this time. A character song album for Saki will be releasing, but since this show has a moderately large number of characters, only the fifth player in the rotation of every team will sing.
Thus, the listing (a fairly nice selection of VAs) is:
Kiyosumi: Saki (Kana Ueda)
Ryuumonbuchi: Koromo (Kaori Fukuhara)
Kazekoshi: Ikeda (Rika Morinaga)
Tsuruga: Yumi (Yuu Kobayashi)
This is all that's known for now, and if there is more news, I will, of course, report it.