https://twitter.com/UltimateFreak91/status/464421056095059968
Update: Shinobi clarified after the article was posted that he meant that Sony Bend isn't working on Kill Strain. So it's still possible that they're working on a new Syphon Filter, but their new title is not related to the Kill Strain Trademark. The article has been amended to reflect that.
http://www.dualshockers.com/2014/05/08/sony-bends-unannounced-ps4-game-isnt-syphon-filter-but-something-great-according-to-insider/
Update: Shinobi clarified after the article was posted that he meant that Sony Bend isn't working on Kill Strain. So it's still possible that they're working on a new Syphon Filter, but their new title is not related to the Kill Strain Trademark. The article has been amended to reflect that.
http://www.dualshockers.com/2014/05/08/sony-bends-unannounced-ps4-game-isnt-syphon-filter-but-something-great-according-to-insider/