I agree that a buyout is not going to happen. It's just *way* too much money for them to spend all at once when they're still under shareholder scrutiny, and their hardware is selling under par, and they're obliged to turn a profit next year (although they could afford it without worrying too much, and savvy Nintendo shareholders might recognise the long-term benefit of a buyout, but that's a serious long shot). However. Acquiring Capcom's superb staff and IPs would be a tremendous coup if Nintendo intends to stay in videogames for the next 15-20 years, which I'm sure they do. Anyone pointing to Capcom's lack of daring, consistent output outside of RE and MH should realise that Capcom has relatively little cashflow compared to Nintendo. They're terrified of spending money. Being a division within Nintendo (and I'm sure they would be, they'd surely keep the name and logo) would alleviate that to an extent, giving them production leeway, and a chance to actually find out if their IPs can still sell. If you can only get Nintendo and Capcom on one piece of hardware - you've basically almost all of gaming's most iconic characters and franchises all in one place. That would make for unmissable hardware to hardcore gamers, the kind who buy hardware for those few or even that one magic franchise. And when you launch hardware, they're the buyers you can count on.
And this is going to sound really lame, but it's obvious that Nintendo simply likes Capcom a lot, their way of doing things, their games, and what they mean for the Japanese games industry. I've no doubt that they'd rather step in than allow an indifferent entrepreneur to do the same and hack the company to bits.
The reasons 'for' are certainly there. It could work. But would it be worth the asking price for Nintendo? Long term, yes. Right now? Probably not.