Want to know more about quorum technology -> https://en.wikipedia.org/wiki/Quorum_(distributed_computing)
The problem with decentralized exchanges is that some entity must have a bank account in order to do the Fiat > Crypto or Crypto > Fiat conversion. In the future, if we can close the loop and lessen the Crypto > Fiat trades, then a decentralized exchange might have a chance. But a decentralized entity cannot set up a bank account to convert to/from fiat.
You could sell crypto in a marketplace such as open bazaar, have the crypto in escrow until the money clears. But if it were hosted on the Masternode network (the open bazaar) then I fear masternodes would be held accountable for money trading.