Western studios are already accounted for PS4. Manchester Studio does seems to move to PS5 as we are not getting more trade shows than TGS this year. When they opened North West Studio in 2015 they said it will focus on games for Project Morpheus. Blood & Truth from London Studio was announced last year and will come out soon.I recall that after Sony announced they would be focusing on 4 games for E3 2018 (Spider-Man, TLOU: Part II, Ghost of Tsuhima, Death Stranding), Shinobi posted that next-gen PS5 games were in development but not ready to be shown yet. So even if they're quiet about it, 1st Party studios are already at work. No need to worry there.
North West changed to Manchester Studio and nothing has been heard since then. Have they changed their mind? Will they make a PS5 game instead of PSVR? I have that feeling after Shu said there are more unannounced PS4 games in development and TGS will be the next trade show and nothing announced for PGW. SIEJA is changing their format from press conference to a live video show similar to E3 to give viewers a experience in these worlds and storytelling.
Andrew Goldfarb from IGN is now in Tokyo after Gamescom. They were the ones who did the full interview with Shu and Allan Becker at Japan Studio last year where Becker teased new titles in development that are being made with new technology in mind.