So since we have Rise of the Ronin and Steller Blade have both been confirmed to have help from XDev/External development and both look great.
Who else would you else Sony to work with?
Most of them won't happen but if I had to choose:
XDEV Japanese team (former Japan Studio team)
From Software (Bloodborne 2)
KojiPro (Metal Gear spiritual sequel)
Bokeh (Gravity Rush 3, new IP)
Nagoshi Studio (new narrative focused IP without yakuzas or samurais)
NanaOnSha if still exists (Parappa The Rapper sequel)
Enhance Games (new puzzle IP similar to Lumines and Tetris Effect)
Platinum Games (AAA no GaaS hack 'n slash new IP by their best team)
Arc System Works (Demon Slayer)
XDEV America (former Sony Santa Monica team)
Future new studio with key RAD devs who worked for Sony (The Order 2)
Annapurna (LocoRoco)
Ember Lab (new IP)
Supergiant Games (new IP)
XDEV Europe (former Liverpool Studio team)
Stray's devs (new IP)
Roll7 (new IP)
Ballistic Moon, ex-Until Dawn devs (Until Dawn 2)
Sumo Digital (Sackboy 2, Little Big Planet 4 campaign as Dreams big standalone DLC)
Quantic Dream (new IP, Heavy Rain 2: Jason's Revenge)
Remedy (new IP)
Honeyslug (super psychodelic and weird new IP)
Arrowhead (Helldivers 2)
Rockstar North (Knack 3)
I would like them to work with South Park Studios... however Ubisoft has the engine for that I believe.
South Park: The Fractured but Whole was developed by Ubisoft San Francisco using the Snowdrop engine, same engine as The Division, Rocksmith+ or Mario+Rabbids.