What someone should really do is start an exchange with no vig and set it down right in the middle of Manhattan.
As far as I understand it, gambling is not federally illegal and setting up an exchange is not either as long as you do not take a vig, fee, etc...
This is how the 1.5 million dollar pool on march madness has existed for years in NYC. Ran into problems when they started taking a cut.
With a gigantic US exchange, imagine the profit from interest.
I'm no lawyer, but as far as I know, no vig, no fee, no membership, no rake, and you are good to go federally... Dont rely on this advice anyways.
Sean