According to a tweet by ex-senior editor at Game Informer journalist Imran Khan, Bethesda was in talks with Sony regarding Starfield being a PlayStation exclusive:
FUN NOTE: Sony had been negotiating timed exclusivity on Starfield as recently as a few months ago. Going to guess either those talks are done or the price suddenly went way, way up.
With Microsoft now in control of Bethesda, this idea is almost certainly off the table now. Fortunately for PlayStation fans, it's unlikely that they'd make it an Xbox exclusive, either. Microsoft's strategy over that last few years have been focused on expanding their gaming influence beyond just their consoles, creating a larger PC game selection from previous exclusives, and establishing cloud gaming on mobile with Game Pass. It would fit perfectly with their recent behavior to have Starfield release as a multiplatform game.
Granted, it will still be a rather long time before Starfield is released. Right now, the only thing we know about the game is its name and genre. We've not seen any art, animation, gameplay, cutscenes, or anything. It's possible that the gaming industry will be different then. But until then, we remain confident that Starfield will release on everything.