Seems clear he is doing this to increase his personal brand as the "real life tony stark" as opposed to it actually being useful for engineering. His personal brand is an enormous asset on the balance sheet of his companies, so I really respect this - but lets call it what it is.
Of course this will be useful for engineering. Maybe not in it's current state but in future, better versions. He and his team are trying out some really cool ideas. While most of us work on apps that involve displaying text and pictures, this guy has the good fortune to be able to play with rockets and cars etc. Good for the World that not everybody is working on another app.
Couldn't agree more with that.
I'm just explaining the reason you are seeing this is primarily for PR purposes -- which is a huge part of his job. HN should be able to tell the difference between good PR and good tech.