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.
Unfortunately that's not guaranteed to always be the case. The "Trusted Computer Group" already have ways for network operators to answer "Who and what’s on my network?"[0], and it's possible to set up an IPsec VPN between your device and the ISP where the key is only known to the TPM on your device.[1]
Of course the user could try to proxy requests from an "untrusted" machine to a "trusted" one, and piggyback the connection, but I imagine that applications which allow this won't be allowed in "secure" app stores, and "secure" operating systems would in any case firewall off packets coming from "untrusted" machines in the first place.
[0] https://trustedcomputinggroup.org/work-groups/trusted-networ...
[1] https://wiki.strongswan.org/projects/strongswan/wiki/Trusted...