I gave an example in the previous post how the identity of the user could be hidden from the service.

In both your examples the government service has your full identity, then pinky promises to forget it.

Unless I'm misunderstanding something?

It would be a lot easier to get that information from the ISP.

Not quite the same, as IP addresses are shared through NAT, VPNs exist, etc. With the proposed legislation it is illegal for website operators to deliver content to known VPN ips, as they cannot confirm that the end user isn't a EU subject.