Idea is good. But one day FBI will knock on your door, steal all your money and next day dailymail will publish a report that your exchanger was used to do child porn and money laundering. Check how they destroyed liberty reserve.
I checked Wikipedia, it says:
The United States charged founder Arthur Budovsky and six others with money laundering and operating an unlicensed financial transaction company.
it says "unlicensed" and it was in Costa Rica.
You are making a good point, so for this to do not happen again we have to operate such company within USA and comply to all regulations. Not sure if this this "technically" viable though, not a lawyer.
We need to put this idea into reality ASAP because this is the only brake for cryptocurrencies to become widely accepted.