We already have proven, well defined method of DNT already: private browsing. You are still being tracked with private browsing. You IP, user agent, OS, screen

We already have proven, well defined method of DNT already: private browsing. You are still being tracked with private browsing. You IP, user agent, OS, screen resolution, etc. are enough to connect the dots in most situations. This is a decent idea that will need to be implemented to some degree if sites are eventually going to support under-13s, since it is illegal to track their behavior under current law. But you are right, I don't see a lot of places voluntarily signing up to make less money.