Found a schedule for release of the upcoming DLC costumes… well, the ones we know about.
17th April - Nene and Gracia
17th April - Pack of Nene, Gracia, Mitsunari, Ina and Ginchiyo
24th April - Kai, Naotara and Aya
1st May - Koshosho and Hayakawa
1st May - Pack of Aya, Koshosho, Hayakawa, Kai and Naotara
The source baidu thread has the individual CGs on white backgrounds, for those interested!