A briefing from cnn on the exchange wars:
That deal sparked a wave of consolidation -eat or get eaten. The name of the new game is volume: The more trades flowing through your electronic platform, the more revenue. Now the mega-exchanges are each trying to dominate its niche of global trading. The result will be monopolistic empires that keep adding complementary pieces. "The way I think about it," says S&P analyst Jason Willey, "it's a huge land grab."
The barriers to entry are high so this industry will give you few to choose from if you want to own a piece of it. It's all about the stodgy SRO's going public, being disassembled and rearranged; creative destruction.