If you can agree to contractual terms by clicking through some agreement, you can agree to "waive" your DNT setting
In the US and UK, the requirement for a contract to be enforceable in court is that the side wishing to enforce it must demonstrate that a meeting of minds has occurred. It's far from a binary decision. Some things, such as witnessed signatures at the bottom with each page initialed, have large amounts of case law backing them up, so you need a very strong argument if you want to discount them. For click-through licenses, there's a lot less case law and everything on the opposing side helps. If you can demonstrate that you have actively opted out of tracking and then been presented with a click-through license that, buried somewhere in legalese, there is a permission to track, it's easier to argue that the contract is invalid.
Either way, I am not sure what court is going to protect you from malicious actors that would not follow DNT.
The various European data protection offices would be a good bet.
We should be working on stopping the ability to track, not about making statements of intent for possible future litigation in a court of law.
Making it impossible to track means making clients indistinguishable, which is very hard. Making tracking without consent illegal is much easier, because the companies that you really worry about doing the tracking are the ones with large and expensive data centres where they can process the data, and these are nice big targets.