I'll amend my previous statement to say that the tax has a snowballs chance in hell of passing, but not the age verification.
You can't do true age verification without requiring someone to submit personal information.
The courts have ruled again and again that requiring someone to identify themselves in order to view constitutionally protected materials is unconstitutional because of the "chilling effect" it would have on free speech.
The tax, eh, maybe they could pass it, but that in conjunction with 2257 would send all of the major players in this business offshore. Then they wouldn't be subject to the tax OR 2257 which would end in the government having even less control over the adult internet than they do now. That's probably not what they want.
PLUS even if the tax did pass there would be TONS of legal and accounting tricks in play to get around it. "Get all these porn sites for free when you sign up for our $40 a month news service"....etc etc
 
