That would be up to Google to release, not Apple. True, Apple would have to approve it for distribution in the app store, but there is no reason they shouldn't do so. There are plenty of other mapping apps out there.
Ask Google when they intend to release one.
Apple had very little choice but to terminate their agreement with Google and come out with their own maps app. Google was refusing to allow the kind of features that customers were demanding (turn by turn directions for one) because they wanted to give Android a leg up.