It won't break the web any more than not supporting <blink> tag or deprecating SHA-1 certificates anymore. It would affect a tiny minority of sites that try to

It won't break the web any more than not supporting <blink> tag or deprecating SHA-1 certificates anymore. It would affect a tiny minority of sites that try to do weird things. Seriously, we had a lot of JS APIs being gradually deprecated (and, yeah, breaking the web), and we're still alive. And for the last ten years every web developer was constantly told to not depend on User-Agent headers and do capability checks instead of UA detection. If there are still some sites doing that, and a reason for a change exists - it's good time to break them and only make work with some compatibility mode. And those were just the examples. Sure, the trackers will switch. ETags and CSS fingerprinting and any other tracking methods can be worked around too. We just have to start value privacy a bit more than dancing bunnies. (But, sure thing, users want dancing bunnies, not privacy)