I'm not sure if bitshares decentralized asset exchange is going to be the first fully decentralized (OTC) market allowing crypto-traders to trade FX or CFDs but is it possible for fully decentralized FX trading or CFD trading to exist with or on the bitshares asset exchange? Is this the point of bitshares?
IMO no man-made system can be fully decentralized. I like to think of it on a scale of 0 to 100, with 0 being fully centralized and 100 being fully decentralized. Nothing is a 0 and nothing is 100. All financial systems fall somewhere in between including fiat currencies such as the dollar or euro. The real question we should ask is, "is it sufficiently decentralized?" Actually, I would take it a step further and ask, "Is it sufficiently secure?" because cryptography provides a large portion of security but is not directly tied to decentralization. The end result should be a system where users cannot get their assets stolen or transactions censored, either directly or through inflation of the base asset. For example, when your brokerage will not allow 500:1 leverage, that is a direct result of censorship, meaning the system you are using is not sufficiently secure. Also, when the fed starts another round of QE, that is inflation of the base asset which is also not sufficiently secure.
Right now, only bitcoin and related 1.0 technologies are sufficiently secure. Nxt may be the only technology that can be considered 2.0 and sufficiently secure, depending on your perspective. Bitshares, ripple, stellar, and ethereum are not sufficiently secure at this point, but plan to be in the future. The main difference is that only bitshares will offer sufficiently secure assets (bitassets which are pegged to the value of physical world assets) other than the native currency.
This is still very much a work in progress. I am guessing that in less than 5 years you will be able to do this:
in a sufficiently secure environment powered by bitshares... at a fraction of the fees... using 500:1 leverage... trading corn, wheat, copper, usd, jpy, chk, ect, ect, ect. At least that is the plan.
disclaimer: This is still and experiment. No guarantees.