Article is from May but received no attention, and I believe most people are unaware of this; the Mac needs an iBoot on the internal drive in order to boot from any volume, and thus cannot boot from an external drive if the internal one has failed.
Once again Apple is showing how to do things stupidly. They won't allow you to boot from an external HDD/SSD if the internal one fails. On top of that they make it extremely difficult to replace the internal disk on your own. Carbon Copy Cloner has been my number one program all these years, but I think that Apple is pushing us loyal and technical competent people away. They just want "simple" users.
To be fair if you or your company are dumb enough to buy these devices your probably also of a mind to take it in for expensive repairs.
Its perfect business logic from the fruity chaps.