It's there and works fine. It's characteristic type is 00000030-0000-1000-8000-0026BB765291.
It's absurd for this property to be deprecated as it's the only real way to tell accessories apart if the user has multiple iOS devices, and also the only way to remember which accessory the user was referring to later if they configure something in the app, especially since accessory UUIDs are totally unreliable changing frequently even from simple things like deleting an app and installing a TestFlight version of the app.
I think everyone is just assuming if they ever actually deprecate it, they will provide an equivalent replacement. All the hardware people are still required to set it, so it seems there is no reason whatsoever to remove it.
Maybe we should file RADAR bugs about this now so that it either doesn't get deprecated or is replaced with a proper solution that is not totally broken like accessory UUIDs.
>All the hardware people are still required to set it
Don't conflate specific MFi licensing requirements and vendor firmware update schemes with general developer needs.
As always, devs are encouraged to file bugs to help make themselves heard - be sure to add your report #(s) here for reference, thanks and good luck.
Apple confirmed that they do not anticipate the characteristic itself will be removed from the HomeKit Specification. Currently this characteristic is marked deprecated from iOS API point of view, which means 3rd party app client/manufacturer app may not have access to this in future and they dont have a replacement for this!