Sony buying one huge group like Capcom, Square Enix or Kadokawa is possible if the acquisition craziness continues. It's definitely not something they wish to do (too expensive for them in normal circumstances), but the risk of multiple publishers skipping Playstation platforms in favor of promoting other platforms or services might be high enough and can cause some serious damage to PS5's potential. I doubt Sony likes the sound of this. It's a shitty trend, but the more get into it, the more the established players will want a piece of the pie to secure their future in a world where Google, Amazon, Tencent, and Netflix are part of the game.
I'm in the opinion that they'll be safe and remain quite dominant without any major acquisitions, I think most companies acquired by 3rd parties won't skip Playstation. But a little bit of paranoia could be enough to push Sony in joining this madness. They CAN buy significantly bigger groups than Zenimax, but they have to be very careful about it and be sure the price is worth it.
What needs to be considered is the reason behind any acquisition if it to protect themselves from losing access to 3rd party titles then a full acquisition isn't the only option. they could hold enough stock to prevent a takeover whether that's by owning a 51% stake or make alliances, another strategy would be to lengthen existing publishing deals and for non published content the use of more general contracts based on ensuring future content.
I doubt Sony is gonna pay a few billion dollars for something as humble as securing the mutiplats they're already getting. Would make more sense to add a few more billion dollars and gain 100% the revenue and complete control.
"Okay, Capcom no longer supports our platform because [insert platform-holder] bought them to promote their platform (like Zenimax!). We respond by making all of our Square Enix products exclusive."
It's the shit from nightmares, but not entirely impossible. Gaming is arguably Sony's core business now.