Since device_trackers really are binary_sensors, can we include them in the newly created helper groups?
Device trackers are not binary sensors… they can have many states if you have set up Zones.
Device states
The state of your tracked device will be
'home'if it is in the home zone, detected by your network or Bluetooth based presence detection. If you’re using a presence detection method that includes coordinates then when it’s in a zone the state will be the name of the zone (case sensitive). When a device isn’t at home and isn’t in any zone, the state will be'not_home'.