How can I sync the new "people" (face recognition) metadata across devices in Photos (iOS 10 and MacOS Sierra)? The new Photos updates for iOS 10 and MacOS Sierra includes a much more powerful and integrated approach to organizing photos by who's in them.  It's built around powerful, on-device facial recognition.

But once it does its automated thing (finding the faces it thinks are the same person), there's still a lot of manual merging and labeling to be done if you have a lot of photos and are as obsessive about organization as I am.

For example, if you have, say... three thousand photos of your daughter, Photos will find almost all of them, but may guess they're 5 or 6 different people.  So you have to merge the buckets that all are one person, assign them a name (so you can search by it), etc.

But unlike other changes (edits, deletions, organization into albums, etc.), manual changes to "people" data don't seem to sync at all by default.  



Is there really no way to do this?  It seems bizarre that one of the flagship features Apple's touting in this Photos update doesn't play at all with what was Photos primary selling point over iPhoto - everything synced on all your devices.
Before High Sierra release (and the corresponding iOS annual release) this metadata did not sync. Now that data does sync.
Macworld speculates on the reason behind it:

It’s not clear yet whether [facial recognition data will ever sync] because Apple’s push at its recent [2016] Worldwide Developers Conference was for local analysis of private information that’s never uploaded to the cloud.

I haven't watched it myself, but apparently Phil Schiller and Craig Federighi stated on John Gruber's The Talk Show that it will not happen, that the features are device-specific and will not be synced via iCloud.
Edit: The help file for Photos in macOS Sierra was updated with this:

Note: People identified in the People album are not synced across devices.