We heard about it in March, but at today's press conference they revealed more outfits, and the play's site is up and running.
Runs in Kyoto/Tokyo from June 11th through June 26th, doubled casting in West and East versions.
Wikipedia nicely describes this as a space opera manga and details are sparse.
It also does not help that (a) the musical looks more like a seriessquish of both the original and the sequel; (b) there is no Truth/Reverse doubling of the cast, since this isn't a Suemitsu Ken'ichi directed play (he did Joan of Arc for Berryz/Smileage in 2013, and the Trump/Lilium/Specter series in 2014); © they dressed the girls across the two different versions in both the press conference and the web page; and (d) it's late at night and I have bureaucratese to write for work, this is not helping.
Anyway. Cast list below. I went a bit liberal with the name translations.
*Tadatos (Tada) (W) Haruka (E) Ayumi
*Frol (W) Sakura (E) Haruka
*King Mayan Baceska (W) Masaki (E) Mizuki
*Doricas Soldam (Fourth) (W) Ayumi (E) Sakura
Chuchu (Fourth's sister) (W) Maria (E) Miki
Ona (W) Mizuki (E) Maria
Red (W) Kishimoto (E) Erina
Tomano (Baceska's brother) (W) Ogata (E) Masaki
*Mule (Glen Groff) (W) Yamagishi (E) Akane
Lon (Fourth & Chuchu's uncle) (W) Iikubo (E) Ogata
Atenai (academy instructor) (W) Erina (E) Iikubo
Count Aman (Baceska's ally) (W) Miki (E) Asakura
Duma (no idea about this one) (W) Akane (E) Ogata Risa
Ombres -- Shiotsuki Shuu
Minister Papa -- Misa Noelle
Tada, Frol, Baceska, Fourth, and Mule are part of the original 11 cadets.