One issue Sony is going to continue to have is that there are basically only four third party publishers that are capable of moving lots of hardware as far as I can tell.
There's Square Enix, who has several major flagship titles and a variety of mid-tier games.
There's Capcom, who is fading, but still manages to pull in sizable audiences with Monster Hunter and Resident Evil.
There's Level 5, who has shown an ability to consistently launch major children's properties.
And there's Bandai Namco, who usually doesn't make titles that individually sell a lot, but makes so many games catering to so many different niche interests, that having heavy support from them brings a ton of small audiences to your platform and gives everyone a steady stream of games to play.
While other publishers can help, you want several of the primary players for your platform to be successful.
Nintendo, of course, is also a huge draw, but they're obviously not going to release games on PlayStation platforms.