> Electricity I don't know how you could deliver ads through

Even if you could, electricity is a utility with laws against disconnecting it in certain circumstances, even for nonpayment, and the internet isn't. So unless someone is going to make the argument that neural implants are utilities, ads injected into them seems like a pretty fair bet unless there is legislation not only making it illegal to do so, but making it illegal to make an implant even capable of receiving or displaying one. At least with that even if they repealed the law you'd be safe if you already had the implant.