After fresh install of Windows 10 on the new HP Pro x2 612 G2, including all posted/latest drivers, I have no gyro / accelerometer capabilities on this when the keyboard is detached. I have modified the registry so that the SensorPresent and Enabled fields are correctly set in the AutoRotation setting, and I do see the RotationLock field in the display settings... But even with the rotation lock disabled, there is no rotation. I loaded a game to see if the accelerometer was working in other apps... it was not. On a few occassions I can turn the tablet sideways and load a magazine app while sideways, and the app with orient itself correctly. So it seems the accelerometer hardware is there and something can read it.
Maybe the driver is buggy (the tablet model is very new), but you can imagine the difficult of having a hyrbid device that can't rotate. Please correct this...