I don't know if this been thoroughly discussed, so write it here. What if an exchange for example BTC38 act this way?
* create an IOU, for example BTC38.BTS, issue say 37 billion of IOU to a self owned account, for example btc38-market-watcher
* btc38-market-watcher set up a sell wall in DEX's BTC38.BTS:BTS market at 1:1, so anyone can convert her BTS to BTC38.BTS at 1:1
* btc38-market-watcher set up a buy wall in DEX's BTC38.BTS:BTS market at 1:0.9999 with all the BTS it bought from the same market, so anyone can convert her BTC38.BTS to BTS at nearly 1:1
So each outstanding BTC38.BTS is backed by one BTS on the buy wall
* BTC38 create another account for deposit/withdraw, for example btc38-d-w-account
* anyone can transfer her BTC38.BTS to btc38-d-w-account, as a deposit method, then the amount transferred will be shown in the user's personal inventory on BTC38's website.
* same way, users can withdraw from btc38
* users can trade BTC38.BTS on the central exchange
So balance of btc38-d-w-account is actually how many shares are trading on BTC38's central exchange
With this way, co-op can still be traded on external exchanges. And, the exchange can also vote with the co-ops. The steps are a bit more complex than current one, but looks like practicable. The exchange has no risk, users of the exchange bear all the risks.
I think a percentage-based order-filling fee on co-ops (to the network) would be a real barrier for this behavior, however the exchange can always transfer this cost to the customers.
Thoughts?