A little late, but here it is:
Sponichi is reporting that the Marines decided on August 31st to go with Norifumi Nishimura (currently the team's head coach) as their next manager. According to a number of people close to the team, the selection has already met with approval from the team owner and a full announcement is planned at the end of the season.
For the first time in 16 years, the team will have a "homegrown" manager. Nishimura spent 16 years with the Marines as a player and has been a coach with the team since 1998 (head coach since 2005).
=== Update 9/2 @ 11:33am JST
The Marines are also looking to tap Michio Aoyama (currently working in the Marine organization but does have experience as a base coach and OF coach) as head coach and Yoshihiko Takahashi (currently the team's batting coach) as Ni-gun manager.
Hideo Nomo was also a consideration, but he turned down the Marines by saying that he had other things he wanted to do.