The only one that really makes sense to me is Namco-Bandai. First, the two companies have an established history of collaborating on titles to mutual success. Indeed I'd say that their strength lies more in development talent than valuable IP. Still, it just so happens that among their IP is one of, if not the most, iconic video game character of all. And the fact that Pac man fits in quite nicely with the Nintendo character design philosophy makes it even sweeter for both companies.

Konami and Capcom don't seem likely because several of their most valuable franchises skew mature and are graphically ambitious - Metal Gear Solid most notably, but Resident Evil too, among others. I'd rather play games like that on my PS4 or future console than on my WiiU or whatever Nintendo does next. Street Fighter as well is a property that doesn't really conform with the trajectory of design and corporate cultural philosophy that Nintendo have been moving along for the past decade or so.

Sega doesn't seem too crazy, but, again, they have IP (total war for example) that don't make sense for Nintendo. Sonic is a popular character but I'm not sure how valuable he ultimately is. He has his adherents to be sure, but (and this is just speculation) I would guess that the majority of them have a history with the character that goes back to the nineties or early 2000s. I don't believe sonic is a cross-generational character in the way that Mario is. He's very much of a specific time and place and thus not likely to grow in value over the years

Rare makes no sense at all. What would they be buying? The development talent hasn't been stellar in years to put it gently, and they have next to nothing in IP other than Banjo and Conker. Given Nin's history of censorship I think we could safely say that one of those two don't really belong in the house of N. You can guess which one.

If this is true (and I'm VERY skeptical), I just can't see any company other than Namco coming out ahead after a purchase.