I hope it wasn't on the driver's side! :p

As a senior citizen, when we go someplace, I feel 2 sets of eyes are good with all the traffic these days. If I want to sew, I will stay home.

I have trouble sewing well in my house let alone in a moving vehicle!

No kidding! Enough bodily harm comes from loose objects in the vehicle. A rigid one affixed to a dash board without an air bag could be deadly. With the force behind a deploying airbag, it most assuredly is.

I'm guessing the photo you saw was the one that was actually in the passenger seat of a Class A or B motor coach. There is a drop down table there as one more clever workspace in the rig.
Never ever would recommend it while moving, because the machine could kill you even with a slam on the brakes, let alone an accident.
If you are talking hand stitching, I've done it all in the car, still would if my eyes were better. :)

If it is permanently attached to the car, no, not a good idea for reasons already mentioned. But if you can attach it and work in the car while parked and waiting for someone to finish 'whatever'. then why not?

That would be the ultimate multi-tasking!:D I would never even think of using a machine in a moving vehicle, no matter how well it was secured!

That is a bad safety factor especially with the air bags that could explode if you are in a car accident.