GPC (Global Privacy Control) is the header that's actually being enforced in (parts of) the US. DNT is considered deprecated by many, due to the nonconsensual way that Microsoft rolled it out.
It's like saying having a secure OS/browser would deprive malware authors of revenue, and thus vulnerabilities should be preserved unless the user explicitly opts into patching them.
This combined with governments ignoring it, and actively enforcing GPC... it's questionable whether compliance is necessary (I still suggest treating it the same as a GPC signal).
But future work and effort should be put towards the GPC signal.
An approach like this seems ideal to me, the problem is that it's only natively supported in Firefox. Our instructions for Chrome and Edge are basically "install Privacy Badger."
And Safari is the WORST, which as an Apple customer it pains me to say. Not only does the browser not support it, there are ZERO Safari browser extensions, NONE, on ANY platform (mac/iphone/ipad), that you can install that will send a simple GPC signal with the HTTP headers. There is a paid Safari extension on iOS called ChangeTheHeaders that you can configure to send a GPC signal, but come on, you can't ask normal people to buy an app and manually enter a specific HTTP header. (ChangeTheHeaders is made by Jeff Johnson, the same dev as StopTheMadness. I asked him whether he'd consider adding user-friendly GPC signals to that (or any other) plugin and he said it would just be "duplicating functionality" :-/ )
California's "Opt Me Out Act" (AB 566) requires that by January 1, 2027, internet browsers must provide a built-in, easy-to-use setting that allows users to send an opt-out preference signal, such as Global Privacy Control.