The BMW post makes reference to the driver trying to select neutral but the car refusing to do it. A lot of auto boxes won't drop into neutral at full throttle, and I heard a similar report a few years back where a copper recovering a stolen Porker ended up smashing it into a house because whoever had stolen it had sabotaged the throttle to jam (well that was his story, anyway.)
As for turning off the ignition, that's fine if you're on a very straight stretch of road and are sure that the steering will lock in a straight line. Personally, on a motorway, I'd do that and take the chance of glancing off the Armco rather than running out of control until I had no alternative other than to hit something very hard.
Of course, with a lot of Renaults, you're at the mercy of the magical stop/start button, which I'm pretty sure won't allow you to switch the engine off if the car is moving (I think I tried it in my
a couple of times when the engine went into limp home mode, and I always had to bring the car to a complete halt before stopping and restarting the engine.)
So a Renault with the stop/start button and automatic transmission probably leaves you out of options if this happens. Maybe it'd be an idea to have a driver-accessible 'kill switch' on these models (though that won't help if the dCi decides to start using its own sump