If I was them I'd buy Kadowaka (including From Software), Bluepoint, Kojipro, Housemarque, Remedy and Quantic Dream.
Other than these teams, I wouldn't buy anything and instead I'd invest on growing the workforce of their already existing development studios in order to have a 2nd or 3rd track team inside the studio and/or having a bigger headcount per game, with the goal of being able to get more games from each internal studio every generation.
They also have an insane portfolio of movies, tv shows and anime. I think they should turn Crunchyroll into the ultimate anime streaming service putting all their related content there and merging it with other related services they may have (as I remember they had at least other one), and to make sure they milk better their movies and tv shows in the other services like Netflix, HBO, Prime Video, etc. Or to make their own Disney Plus merging all their movies, tv series and anime, and related video streaming services they own, into a single service to compete against the other ones and to get a bigger revenue share of streaming their content.
Retrogaming and game subscription markets are growing.
So if they buy Sega and sell or close the Pachinko part, they could have in addition to their currently popular IPs a ton of classic ones from Sega and Sony consoles plus arcade, which could work well for exclusive PS Now streaming and download content, plus maybe some compilations, remakes or reboots.
Same goes for Microsoft, Nintendo, Tencent, Amazon or Google. Yes, they can sign exclusivity deals. But this would end if somebody else buy them. Microsoft and Tencent have been pretty agressive recently buying companies, Amazon and Google need catalog to grow their streaming services and Nintendo well, who knows. It would be a great fit for Nintendo but in many areas always have been behind the other ones and choosing their own (successful) path, as can be now with game subscriptions or trophies to name a couple of them.