@Terrificli -- China isn't the only nation excluded -- two that should arguably be members are India and Brazil. It would appear that emerging economies need not apply for membership. Whether excluding them is a mistake is a question that will likely remain unanswered for some time.
Meanwhile, the aforementioned nations with emerging economies will probably want a say in the shaping of the global economy. We can only sit back and watch events unfold.
Of course, one must wonder how effective groups like the G7 and G8 actually are. In the United States, for example, the Federal Reserve has more control of monetary policy than any international group likely will in the near future.