I could see Nintendo maybe shelling out to secure a small western studio like Next Level. They've worked pretty well together on Mario Strikers and Punch-Out (both critically and commercially), I can see Nintendo furthering the relationship and sealing the deal. Especially now that NST's seemed to have imploded.
Outside that though, I can't think of anyone Nintendo would really be interested in buying out. Nintendo generally seems to prefer starting up new studios with key talent (Brownie Brown, Genius Sonority, Project Sora, etc), maybe they should throw some cash Mikami's way or Matsuno's way and start up some new "mature focused" studios? Hell, Nintendo could probably buy back the Ogre IP for Matsuno if he wanted it too.