The team is working on the API, and we will post as we have more information.
In the meantime, for Embrava, please note they have announced presence support for TeamsOnly mode with their version 5.2.16.Chris Crawford commented
+1 for the core requirement. If I could pile on: The ability to see if camera and mic are live is also important for the best possible status-light capability. These were observable in the S4B client API, and it really helped my implementation of a client-status-indicator. (E.g. Yellow was in call and muted with Red as in call with either microphone or camera live.)