How can ISPs do anything close to this when they're not even concerned with how many devices you have? ISPs just do not connect individual end user "devices", they connect subnets.
> content providers may refuse to serve you
Providers of Hollywood-copyright-mafia content like Netflix have already been demanding hardware DRM (at least for high resolutions) for years.
Providers of public ad-supported content like YouTube care about maximizing views above everything. They'll happily serve a 4K stream to a Windows 98 machine if it can connect with modern TLS somehow. YouTube isn't even trying to fight youtube-dl all that much, there was an attempt at throttling recently but it was very quickly defeated. Heck, YouTube Music on the web does not use DRM at all, and that's all music-copyright-mafia content there.