Nintendo could really use another RPG maker to dedicate for their consoles and make them more appealing. Mistwalker would be an interesting choice. Platinum not so much so, to be honest their games aren't very good.
There's no way they could afford to buy huge corporations like Square Enix or Sega at this point though. Even if they had the means, the costs incurred over the next several years would be tremendous and the stock would plummet. Nintendo is in a precarious enough financial situation as it is. Maybe if Square Enix continues its downward spiral they could buy some of their assets.
Rather than buy another studio, Nintendo could hire more internal development groups focused on new innovation instead. Give them more freedom to develop apart from the traditional Nintendo style. I think this would be a much better idea.
