The rumor started with Ubisoft's financial earnings, citing a new Ghost Recon game to be released before March 2010, specifically Ghost Recon 4. Now, the Australian ratings board has a listing for Tom Clancy's Ghost Recon: Predator, which many are presuming to be the fabled Ghost Recon 4.
To me, the title sounds like a portable title. Resistance: Retribution...Syphon Filter: Logan's Shadow...Killzone: Liberation...you see the pattern. However, the listing clearly states that the game is rated for mature audiences, and has a "CG (Multi Platform)" classification.
I'm personally looking forward to continuations of the Ghost Recon and Rainbow Six series, both of which have been co-op friendly this generation. Let's hope this rumor rings true.
Source: Destructoid.com