I think the problem with decentralized exchange has always been the fiat link rather than tech. 

There is some hope that some crypto friendly jurisdiction will be issuing their owned pegged crypto, e.g. J-Coin with Japan, that can serve as a fiat gateway rather than sketchy scheme such as Tether.  Once you have a real JPY Tether backed by sovereign, then it's a simple atomic swap or any decentralized exchange, then you can do your usual forex via USD/JPY, EUR/JPY or CNY/JPY pair.