NoJ has been pretty good about training their next generation of talent actually. Splatoon was an idea that originated from their newer staff. Most of the recent Mario and Zelda games have been using more ideas from Koizumi than Aonuma or Miyamoto. In fact, Miyamoto basically doesn't do anything in the game side of the company anymore other than advising, so he's practically retired but cant really even hint at retiring without tanking the stock price.