The exchanges are actually on a weired situation, most of them are aware of the SEC and the different US regulations, remember what recently happened to BTC-E, even if it haven't started from the SEC at least, they reached them outside borders.
I believe this is why Bitfinex is now refusing US customers. There are more regulations every day, different countries are trying or starting to regulate bitcoin and cryptocurrencies markets, this is a serious limitation for exchange listing. Even the ethereum tokens are under regulation threat.
I think you're in a situation where you can offer service to anyone. A public blockchain app, is it even possible to deny service based on country? Since NVO will be 256 bit encrypted and cold storage client side based, you just have to keep out of countries that want to charge you for running the exchange. As long as your host country is fine with it.