> It's the most obvious way of eventually getting rid of per-site cookie notices - make DNT legally enforceable and cookie notices become irrelevant for people who have it switched on.

I think this is unlikely to happen, because most websites actually want to track you. So they will display the banner anyway, or perhaps a slightly modified version like "we noticed you have your DNT turned on, but are you willing to make an exception just for us?"

That gives them a chance users will consent anyway to get rid of the cookie banner. And they will argue that a specific consent given on their website overrides the generic non-consent represented by DNT.