"Are you really suggesting we should be teaching school children how to program an OS?"
If he's not, I certainly am. The point about the Pi is that a few hundred lines of bare-metal code can make it flash an LED, beep a speaker, detect a finger, detect a light source etc etc. And that is where it all starts for kids. On that simple beginning everything else can stand. Over a number of school years, a complete school OS could be built, and the relevant hardcore Computer Science introduced as appropriate. That's how to teach computing.
We have forgotten that an "OS" can be simple and elegant. Of course, any single board computer could have fulfilled this role equally at any time over the last 20 years.The noise and b'llsh't of the likes of corporate MS have perverted what happens in schools. (And for balance, Linux is far too large and complex to play any part of early school learning. These are tools.)