I actually think this is likely. This was rumored a few years ago in the same article with SOCOM 4. The SOCOM 4 rumor was true. Syphon Filter probably is too.
I've never played any of the past Syphon Filters, but I hope this rumor is true. This gen has been lacking in some good ol' Stealth action.
Metal Gear Solid 4 is the only good stealth game I can think of. Splinter Cell: Conviction was a good action game, but it was definitely lacking in the Stealth department. SOCOM 4 turned into a action game as well. Even my beloved Hitman looks to be following the same trend. *sigh* Here's hoping this stays true to it's roots if it does release.