For what it's worth, Apple sometimes don't list Macs as compatible with new features if they don't fully support the feature, or if their performance while using it is underwhelming.
It may be that the devices listed have a faster wifi system than others, which might be required for full-resolution AirPlay to their screen - it's possible be that a direct cable or ethernet connection might enable the functionality, but the inability to fully support the feature keeps them off the compatible list.
All speculation of course, and time will tell if enterprising coders are able to work around software lock-out if that appears to be in place.
It may be that the devices listed have a faster wifi system than others, which might be required for full-resolution AirPlay to their screen - it's possible be that a direct cable or ethernet connection might enable the functionality, but the inability to fully support the feature keeps them off the compatible list.
All speculation of course, and time will tell if enterprising coders are able to work around software lock-out if that appears to be in place.