Yes, GPS of the control station could glean that info from the cell phone or tablet attached to it.I'm pretty sure FAA doesn't say a GPS reveiver has to be actually in the controller, only that the broadcast include the controller location.
It seems likely that DJI could update current Mavics to broadcast RID, but the remotes themselves don't have GPS. The apps rely on the mobile device in providing our location.
I suppose what will happen is if the mobile device is incapable of providing the AC the accurate RC location, the RID will operate as if it were a module even though it's built-in and the app notify the user that they are only type 2 compliant.
And if the user doesn't fly with the app, DJI drones already limit height and distance which would force VLOS.
But it still begs the question, how accurate does the location have to be, since there are alternative means to GPS
The issue would with non-GPS devices like smart controllers.
A lot of the details will be set as we get closer to the implementation. And when ASTM provides the FAA with their standards, even more will be answered.