I'm not sure if the parking brake would be person** enough to bring the car to a halt from speed all the same.
It's an interesting experiment to try. In my experience of finding interesting ways to bed brake pads in

what one would probably regard as quite heavy braking will limit a powerful car at a constant speed in the higher gears.
When it comes to actually stopping it in a useful distance from the worst case scenario where it's accelerated to 80/90 MPH before you realise something's not right. Hmm. :-/ What's clear to me is:
1) You would have to
stand on the pedal
2) You would build up a lot more heat in the brakes than during a normal emergency stop, so you would probably get one shot at it before the brakes faded. If you braked half-heartedly, lifted off and let it accelerate again or anything like that, you'd probably find the brakes too hot to give you a second chance.
3) What happens as you slow and the gearbox, if auto, starts changing down? It would probably overcome the brakes in a low gear, especially if they're hot.
A mate of mine had a Pug 406 diesel which started burning its' own engine oil due to turbo seal failure on the motorway and he said he very nearly left himself with no brakes trying to stop it before he dipped the clutch and let it rev itself to oblivion.
All immaterial if you take the gearbox out of gear, of course. Makes me wonder if gear selection was also electronic and nanny ECU thought "ooh! you don't want to take it out of "D" at this speed!".
I suspect it was more the case that the driver, who would clearly have been at 110% stress level, probably didn't go through a methodical process of trying the ignition, realising the stupid transponder and "Start/Stop" button was no help, then shifting focus to getting the transmission into neutral, then on braking it to a stop, and so on. He probably spent his last seconds hitting the button to no effect. Lack of familiarity with the vehicle may have been an issue, of course.
Makes one wonder if it wouldn't be better to have standard, mechanical controls for the ignition switch and gear selector on all cars. :-/
In addition, if the car had left him several routes to shut it down (ignition switch, clutch, gear selector, etc.) maybe he'd have hit upon one of them in time.

Kevin