tongue_of_colicab
Veteran
It's is unlikely that they go straight to double yellows so drivers would unlikely be caught out.
Left in the drivers hands they won't slow down.
As far as I know the limiter doesn't apply brakes so if it cut the engine until a pre agreed speed is reached then it wouldn't cause any problems cars would gradually slow down to the required speed.
First of all they can't cut the engine because they won't be able to restart them. Lowering revs would be possible but who knows what could happen if you suddenly do that. A more sensible option would be to change the speed they are allowed to drive in the yellow flag section. That could easily be displayed on the steering wheel.