I think in this sense you are simply linking a Plex login to an Apple ID. The user(s) on the Plex server would not need to be changed and could still be used for playback/syncing on other devices.
The changes here would likely require them to have a unique Plex login to take advantage of separate profiles in Infuse.
Support for Plex Home users could be addressed independently of the multi-profile features being discussed here.