Dunno, but at least they'd have an instrument that shows them the data they're being penalized on. NASCAR never announced a speeding penalty as 'exceeding 2200 RPM in 2nd gear'. The penalties are in average MPH. Basing your speed on a tach reading gained while attempting to maintain a constant distance behind another vehicle (likely with other vehicles in between) has always seemed like a shaky proposition.
What inspired this was my attempting to respond to my wife's astonished, 'You mean the don't have speedometers'. I couldn't tell her why not.
They already have a 5 MPH cushion. Regardless of device, they're going to push it anyway.