Some comments seem to be optimistic about the potential change from Apple. But once Apple relax webkit requirement from app store, it will mean all "do not track" cookie enforcement would be easily worked around.
If you want to opt-in to Apple's protective blanket, do so. It's not an excuse to weld over the safety hatch for the rest of us.
Chrome and Firefox might certainly implement it into their browsers, but can we expect Facebook, for instance, to do it in their in-app browsers?