As ever, the existence of the screenshot doesn't necessarily indicate anything new - this could be porting work done to test the RAGE engine (some on GTA Forums have pointed out that the lack of 3D modeled grass could indicate that the screenshot comes from the last-gen version of the game), scrapped content, or a simple passion project on the part of Page.
As for GTA content in the "definitely actually real" zone, Rockstar last week announced "Further Adventures in Finance and Felony", one of the "biggest and deepest updates" to GTA Online, which will allow players to become a criminal CEO when it arrives on June 7. Joe Skrebels is IGN's UK News Editor, and he just won't give up on a new GTA London. Imagine the stereotypes! Bliss. Follow him on Twitter.