I just wanna say real quick, as somebody who's admittedly a bit more open to acquisitions then most, I personally have two main pieces of criteria before I consider the possibility:
1. Do the two companies have a good history with each other?
2. Would it be to the benefit of BOTH parties, not just the one doing the buying?
This is why, when it comes to Nintendo, I mostly suggest they buy companies like IntSys, HAL, Grezzo, and other companies like that. Basically, more stuff like the Next Level Games buyout.
However, with bigger companies, things get a bit more complicated. Especially given Nintendo is somewhat infamously behind when it comes to technical stuff in their consoles. In Sega's case, while the first piece of criteria would certainly fit for Nintendo, the second part... not so much. Aside from being supportive of fan projects, Sega is more or less just like every other game company: always trying to push forward. The majority of their games are on so many different consoles, plus PC, and some of their most recent games are actually rather advanced. So to put them under Nintendo would more likely HURT Sega than help them.
That being said, maybe a sort of... compromise? Like, rather than sell the entire company, they could just sell off certain IPs they have no interest in? I know Nintendo doesn't actually care about the IPs in the acquisition, just the people who make the games, but... I'm just spitballing. Not like anything's gonna happen either way.