Lots of sad sad news this week from US regulators …
First, if you run any type of an exchange it needs to be registered with SEC
And then, if you exchange currency for currency you also become a money transmitter
There is a question then whether there is any way to run any type of a market maker smart contract legally …
This looks like they are closing pretty much all ways to exchange tokens.
An interesting thing is that Ethereum already has an embedded market that exchanges ETH for gas 
I do not think that SEC guys understand this though