In a recent blog post, Marvelous Europe went over in detail about the various editions of Senran Kagura: Estival Versus and the DLC plans lined up for it.
They detail all the goodies that adopters of the Bahonkas Edition of the game will be receiving, including a two disc soundtrack, a dakimakura, specially designed box and several art cards.
On the software end, the game will be updated to the 1.17 version, which comes with a bunch of additional content and bug fixes. They also mentioned that Daidoji and RIn will be included in the game for free.
Ayame, Ayane, Naraku and Kagura will be available as paid content. They also plan to release more content in the forms of missions, costumes, Shinvoi Versus BGM tracks, accessories and hairstyles.
Sadly the Ikki Tousen characters that were released in Japan will remain a Japanese version exclusive. The reason for this is due to licensing issues.
Senran Kagura: Estival Versus is slated to release in Europe sometime in early 2016.