DO_NOT_TRACK support doesn't mean tracking is not an explicit opt-in.

Example: the software crashes, and there is a crash handler that asks you if you want to send a crash dump. With DO_NOT_TRACK, the crash handler is disabled entirely, no question, no dump.

If it gets some adoption, that's probably how it will work. Those who have an financial interest in using tracking (ex: ads) probably won't support such an option.

Most services are already collecting telemetry, them announcing support for it won't change that.

Well, don't look too deep else you won't be using many modern tools.