I've been working on a decentralized futures+derivative exchange for a while and this is certainly interesting to me.

EDIT: The real issue is how to create a fair and coherent distributed orderbook. Will it be on a separate website or set of websites? That would still act like a bunch of exchanges. A truly decentralized model would work at the level of individual users.

A second issue is the credit/anti-credit. Where will it be stored? On the blockchain? As dust? On separate websites?

What prevents someone from simply accepting coins for credit and then no longer participating in the system?

Lots of issues here.