And now there's this:http://next-360action.sega.jp/
There is speculation that this may be a new VO game (EDIT: link courtesy velocity7):http://blog.esuteru.com/archives/430902.html
The page at "next-360action.sega.jp" has little relevant info, other than a cryptic "SIX". Perhaps this a reference to the "VO4" teaser on the Force site when it was first launched.
However, the page source code reveals that the page statistics are tracked by the same Google Analytics account as "vo-ot360.sega.jp". The account number is 902977... vo-ot360 is the 13th site (or Website Profile) under the account, next-360action is the 17th site. I checked a few different sega.jp sites and there are a variety of Analytics accounts, so there is not one "master" Analytics account for all Sega sites (e.g. the account for sega.jp is 11009541, phantasystar.sega.jp is 4938206, sonic.sega.jp is 349115, and samba.sega.jp is 5889575). Another site under account 902977 is www.virtuafighter.jp (3rd site).
It is easy to create a bunch of Analytics accounts using a single Google login, but the accounts will be somewhat separate (the stats will be completely separate). Creating multiple Website Profiles lets you see a breakdown of all the sites on one page, so it's possible each team manages their own Analytics accounts, and thus the "next-360action.sega.jp" is being done by the same team as VF5 and VOOT360.