According to this, MGS creator Hideo Kojima has started work on a “concept for a new game outside of the Metal Gear universe”. The news apparently came from comment made to the Nikkei by Kojima president Fumiaki Tanaka.
Tanaka added nothing other than the fact there won’t be an announcement on the new game this year. For the record, Kojima has talked about working on a new title outside of the MGS franchise since before the release of MGS2. He told us in London just before the second game launched that his mind had many drawers and he only had to open a different one to make a new game. Seriously.