This is the system-version that ships with launch-day JPN New_3DS systems. The TMD HTTP Last-modified date for these titles is September 26, 2014. Note that some of the below might not be completely accurate, since it's actually not possible to tell via checking CDN whether a New3DS title was added with this launch system-version or 9.0.0-20(except when there's two versions of that title).
New3DS System Titles
New3DS versions of the SAFE_MODE system-modules were added, the only New3DS SAFE_MODE system-modules which were not added are: camera, cecd, MP, and NDM.
Besides the 3 new modules below, New3DS versions of the following native system-modules were added: camera, GSP, i2c, MCU, PTM, and spi.
The following 3 new sysmodules were added(not available for SAFE_MODE):
5 new applications for New3DS-only were added. See here regarding the new applications. Besides those applications, New3DS versions of the following applications were added: "Health and Safety Information" and Face Raiders.
The New3DS versions of the following SAFE_MODE applets were added: ErrDisp, error, and swkbd(Software Keyboard).
A New3DS version of NVer was added. Therefore, there could be future New3DS-only system-updates.
Note that the New3DS Internet Browser is not available on this system-version, it was added with this. Trying to launch the browser results in the system going to the system-update section under System Settings.
New3DS versions of all 4 FIRM titles were added.
New3DS FIRM uses an additional crypto layer on the ARM9 FIRM section via a loader at the end of the ARM9 binary, see here.