Can't see how a distributed exchange could work.  Transactions need fast confirmation on an exchange.  If not traders will not touch it and you need traders to provide liquidity.  Imagine being in a fast moving market and taking a long position but not being able to confirm your order was filled until 10 mins after the fact.  That's 10 mins of exposure where your hands are tied.  You can't sell because the counterparty you're selling too can't be sure you've got the BTC to sell them.

Best option is multiple exchanges for redundancy and multiple clearing houses to link them so you make trades across exchanges.  Under that model it wouldn't be so nearly impossible for a new exchange to break into the market because there clients could trade with clients on the other established exchanges.  If not clearing houses then the exchanges need to provide facilities to make arbitrage viable.  The arbitrage traders provide liquidity across exchanges.