Considering this was likely being re-built for the ground up in mind for the PS4, the game must have needed a lot of time to develop.
And considering how packed this E3 was for Sony (remember, both Uncharted Collection, their work with Indie developers and even Ratchet & Clank wasn't that present in the E3 Conference; it was taken over by Horizon, Dreams, third party deals (AC, Call of Duty, ect), Last Guardian, Shenmue 3, and FFVII Remake), Sony must have pulled a lot of stuff from the original conference and decided to save that for future events (Paris Games Show, PSX, TGS).
News will come about this game, same with Sony Bends future project, the new God of War and other 'secret' Sony tittles. But they announced a lot at E3, so they want to save things for latter I guess.
Also, keep in mind that Studio Japan is working on TLG; Sony must want that out the door fast, so they likely have a large amount of the studio working on getting that complete in time for early 2016. So, once that is out, we might get more news on Gravity Rush 2/Gravity Rush Remastered/Gravity Rush Remake early next year.