I didn't mean to suggest that people try to start up exchanges. Just that those already running exchanges who want bigger blocks, like Erik Voorhees or Brian Armstrong, could take actions to pave the way for bigger blocks without waiting for miners.Good idea. Problems:
-Anyone can run a node. It makes little difference how many nodes support what protocol choices.
-There's a big barrier to running an exchange, and an exchange has no direct say in the protocol.
-Only miners matter.
Not all non-mining nodes matter that much, but some can have a big impact. For instance the policy choice supported by the nodes that Coinbase runs could make a big difference.