Also dont anybody think that they dont have a lot of unanounced games left to hold back at this point and this is just pr talk..
Dont know about 2nd party (not even sure if any of froms games is 2nd or 3rd party) but sucker punchs games literally the only 1st party we dont know about right now
At the very least, Sucker Punch and Pixel Opus have had 3 years since they released their last games.
Then there's Manchester Studios, which we haven't seen a game from yet, granted it'll be a VR game. There's also Sony London, who while is most likely doing only VR, could have a surprised home console game in the works.
Then there's the Xdev side of Japan, whether From has a game with them or not, they're for sure working with other developers on games. I also have to imagine all their internal teams weren't on Gravity Rush 2 and Knack 2, so they have to have internal things going on there.
Then there's the chance of second teams we don't know about. Quantic Dream probably has another game to show, but aren't going to show it until Detroit at least has a release date. With how much Supermassive is pushing Until Dawn universe stuff, I'd be shocked if Until Dawn 2 wasn't in development. With how Dreams is going, I wouldn't be surprised if a second team at MM is working on a Tearaway 2 or something along those lines. With how Ratchet did, is what's left of Insomniac working on a Ratchet 2. With the push for something Sly Cooper whether movie or TV, do they have a game to go with it, not from SP, but from someone else.
Sony's First few years of the PS4 relied on external devs, now that we know most of the First Party stuff, and we still don't know all of it, I have to imagine the external stuff didn't stop, besides some iffy spots like RAD.