I personally feel the units should be defined by the driver. I've performed a lot of testing on automotive produces and vehicles. There, the ability to change the units on the display is an error waiting to happen.
I realize there is a different level of data being provided by sensors in HE however I feel the concept is the same. For example ( degrees F, degree F, deg F, °F or F) are all valid units for a temperature reported in Fahrenheit. But they are different from Watts or Amps etc.
I don't even know how one would define the logic for the dashboard to know it can change from deg F to °F but not to watts. One would have to include all the possible unit options.
Again my position is: If there are to be options for units, they should be in the driver.
I'm not a groovy programmer but I would imagine that once a snippet of units option code was written for a driver, it could be leveraged for nearly all drivers with units to be reported.
Just my 2ȼ
John