A much more naive version of this, the Do Not Track header, was removed from major browsers (partly) because it was actually being used for fingerprinting. I strongly suspect a less naive version would be subject to more abuse: as it gets more granular it becomes a fingerprint all on its own.
I understand that you’re suggesting pairing it with legal force, but I also highly doubt that would or could be effective in any kind of consistent way.
I think another reason Do Not Track failed is that advertisers (e.g. Google) didn't like it. Microsoft setting Do Not Track on by default in Internet Explorer was likely the death knell.
The on-by-default setting was technically a violation of the standard, which meant that participants felt they could ignore the setting for IE, which didn't help the initiative for sure.
The industry-led-initiatives are all basically bad, for the obvious reasons. So many of them amount to telling ad networks whether or not the massive amount of data they have collected about you should be part of the consideration for what ads to show (for now) — many offer no possible way to opt out of recording and storing such data in the first place.
This is a situation where legislation is probably the only answer.
>The on-by-default setting was technically a violation of the standard
A standard written for advertisers by advertisers. This is the problem. There are technical solutions, but the biggest advertiser (Google) makes the browser. This is the same as "the revolution will not be televised." The adversary controls the medium.
Attach it with legal force and money, as in allow users to sue for violations, and explicitly permit class actions with the definition of class (all people similarly situated; definition frequently abused by defendants) to be anyone with a browser.
Needs more work,, but the concept is that it needs to incentivize developers to develop track-the-tracker technologies that will catch violators, which then leads fairly directly to a profitable private suit (instead of relying on the overworked govt bureaus to do it).
I understand that you’re suggesting pairing it with legal force, but I also highly doubt that would or could be effective in any kind of consistent way.