The solution here shouldn't be technical; it should be legal.
If we rely on the technical path, Comcast can achieve the same by how many active IPv6 addresses are in use. Even if you aren't using your phone, the device is going to be constantly pinging services like email, and your ISP can use that to piece together how many people are at home.
If we rely on legal protection, then not only Comcast, but all ISPs will be prohibited from spying on their customers. Ideally the legislation would be more broad and stop other forms of commercial/government surveillance, but I can't imagine a world where Congress could actually achieve something that widely helpful for regular citizens.
If we rely on the technical path, Comcast can achieve the same by how many active IPv6 addresses are in use. Even if you aren't using your phone, the device is going to be constantly pinging services like email, and your ISP can use that to piece together how many people are at home.
If we rely on legal protection, then not only Comcast, but all ISPs will be prohibited from spying on their customers. Ideally the legislation would be more broad and stop other forms of commercial/government surveillance, but I can't imagine a world where Congress could actually achieve something that widely helpful for regular citizens.