They're going to have to do something if all these other companies keep getting snapped up by Microsoft. They can't have partnerships if there are no partners. Mercurysteam would be a good purchase, but Nintendo needs to start locking down Japanese content, and fast. Sega would be an awesome acquisition, but I also think Koei Tecmo would be an excellent fit for Nintendo. They're already heavily invested in Nintendo development as it is. They've worked on quite a few mainline Nintendo titles such as Fire Emblem. Their single most successful product is Hyrule Warriors: Age of Calamity. They have a stable of RPGs through Gust. If Nintendo got its hands on Platinum as well, that would put Bayonetta and Ninja Gaiden under the House of Mario.
Let me make myself clear: I actually don't like any of this consolidation going on. I'd like for these studios to all stay independent. But at this point, railing against consolidation is basically pissing in the wind. And besides Sony and Microsoft, we're also dealing with Chinese conglomerates with huge war chests and questionable ties to the Communist Party of China. Better Nintendo than Tencent or NetEase.
Regarding SEGA, one of its flagship studios is Creative Assembly, which makes the Total War games. These as PC games. They also have Relic, which makes a lot of PC only games. I don't think Nintendo would want to also have a PC branch, because then people will moreso demand other Nintendo games come to PC, which they don't want to do. Only way I could see Nintendo buying SEGA is if they do so under the agreement that SEGA West splits off into its own company or is bought by someone else. Maybe Microsoft gets SEGA West and Nintendo gets the rest? I'd love all the Total War games on Gamepass PC, personally.
Don't get me wrong, I'd love Nintendo owning Total War and having officially licensed Hyrule Total War and not some mod, I just don't see Nintendo wanting to own PC studios.