OP quite clearly argues that multi-user systems can still have the old behavior if they so choose with explicit configuration. OP makes an argument about what should be the sensible default in 2022, and who should do explicit configuration.
I think the point that nowadays easy single user linux configuration should be preferred over multi-user configurations is good.
IMO distros could make this easy by turning privileged ports into an (advanced) installation question. Then the clearly single-user-focused distros would default to 80, and the more server-oriented or conservative distros would default to the current behavior, but both could do which ever.
> Start your service on port 8080, for example.
In the era of Let's Encrypt, this is really about 80 and 443. The background for the OP is probably to host "normal" sites on single user hardware.
If you were to give out to non-technical users addresses like "http://example.org:8080" which then transform into "https://example.org:8443", that's just horrible UX. Those kinds of numbers in the URL probably also look to many people like someone is trying to hack them. Furthermore addresses are also communicated word-of-mouth "go to example dot org".
So no, using unprivileged ports is not an actual workaround for the use cases OP is referring to.