The income from anything other than the academic institution as a student is already taxable. Arguably, once a 'student' becomes an employee (which this sort of thing will likely create unless the money comes directly from third parties with absolutely no financial or other association with a school or state (a purely private invididual or business in other words), then existing tax law would almost certainly impose federal income and social security taxes (this is easily earned income by definition). Additionally most states with income taxes piggyback their taxlaws after the federal laws so states will be collecting taxes as well.
I have the impression that the NCAA included language to the effect that if something is done, it would be mostly left up to the states and the conferences as to how and what would be permitted. This the NCAA rightly knows essentially dooms the entire idea to failure from the get-go as there would be no way to get unanimity amongst the 50 states and if the Feds get involved, it would be a complete disaster for all parties concerned.