A) The first web site that decides to block traffic from this site. I can almost see the msg, "You have tried to access this content from an anonymous internet address." Please resubmit your request from a trackable source." Or something.
B) The fact that, being the first of its kind, this ISP is a pretty juicy target for those who oppose such activity.
I suspect the only way to deal with A & B is that multiple such ISP would have to both form and sign-up subscribers en mass. Without such, both A & B seem like barriers to success.