According to O'Neill there are no other emerging economies that are even close in size to the big four. Indonesia and Mexico are the next largest and are well behind.
Right now O'Neill thinks all four of the BRIC countries are facing interesting challenges. But O'Neill doesn't think it is a big surprise that growth is slowing in these countries because over time growth rates do have to slow.
With respect to China in particular O'Neill thinks things are actually going pretty well. The Chinese government has intentionally slowed the rate of growth to focus on the "right type" of growth.