Well, everyone has their own bank account. There's a lot of potential there to just transact directly. You would have to design the deposit layer to be someone efficient though so traders can still use credit. But I think its possible.
To give you an example there is this application called https://bisq.network/ that uses double-sided collateral in contracts to trade fiat currencies. There might be the potential to link this up with SSL, too. I've seen this application that can provide proofs that a page was in your browser https://tlsnotary.org/. Use that to prove a bank transfer happened on an SSL page and you've got yourself a dex that can work trustless with oracles.
To give you an example there is this application called https://bisq.network/ that uses double-sided collateral in contracts to trade fiat currencies. There might be the potential to link this up with SSL, too. I've seen this application that can provide proofs that a page was in your browser https://tlsnotary.org/. Use that to prove a bank transfer happened on an SSL page and you've got yourself a dex that can work trustless with oracles.