Just thinking out loud here but is it possible that places like Y Combinator will end up fulfilling this role in the future?
YC is like a new elite graduate school / bootcamp for startup entrepreneurs. Just like not everyone gets into HBS or Saïd or INSEAD, not everyone gets into YC.
B-school is getting more startup and entrepreneurship oriented, but is still aimed, for the most part, at general management at mid-sized and large mainstream firms.