Ubisoft announced (http://www.ubisoftgroup.com/gallery_files/site/270/1042/1967.pdf) today that it's working on a new Ghost Recon, currently titled Ghost Recon 4.
To quote: Some of our more observant readers likely remember this game coming up in a http://www.joystiq.com/2009/01/22/assassins-creed-2-coming-march-2010/ Ubisoft financial report.
Sadly, it's still a ways off, with Ubisoft crossing its fingers for a release sometime before April 2010.
Doubly sad is the lack of more information at this time, so we don't know if this "flagship title" is more in line with the original Ghost Recon games, or the more recent Ghost Recon Advanced Warfighter series. We'll keep you posted! More PlayStation 3 News...