In release notes for both macOS Mojave and iOS 12, Apple says the
feature has been removed from the initial releases of macOS
Mojave and iOS 12 and “will ship in a future software update
later this fall.”
With the release of iOS 11, Apple also ended up delaying several
features that were initially announced as part of the update until
later in the year, including Apple Pay Cash, AirPlay 2, and
Messages in iCloud, three significant iOS 11 features that did not
come out until months after iOS 11 launched.
Right about now is the time when Apple needs to cut any features that won’t be ready in time for the iPhone launch next month. These delays are disappointing, yes, but I actually prefer this policy of holding off on new features until they’re ready rather than shipping them in a buggy state just because it’s September and time for new iPhones to be released.