I know a lot of bitcoin companies have been having problems with US regulations but those all had a common denominator: they also deal in fiat. If it were only dealing with cryptocurrency I think it could potentially work. And if you are knowledgeable of the subject I would appreciate it for insight, also would I need to do account verifications?
I don't really know if the US Government has any official stance on cryptocurrencies yet. You might have to consult lawyers about this (although I think that they all might have differing opinions on the subject). Also, if you would want to make sure that you can run such a site securely to protect yourself from any external attacks by hackers.