Lol at musks new company called "the boring company".. Digging holes underground ("boring" tunnels) for transportation
It all comes down to funding. He sold investors on Tesla to the tune of 52 Billion. I'm sure he'll find investors for Hyperloop One and the Boring company.
You have to give him credit on a number of fronts. He is very good at engineering management. In the end the team he hires and manages produces results that work. Case in point the Model s and Model 3. That history of results makes investors comfortable and provides the funding for new projects.
Also, because of his celebrity, anything with his name on it will attract the best and the brightest in any field.