This newest proposal - of essentially duplicating the NEC for hyperloop, and all underground - is exactly the sort of reason some people hate/distrust Elon Musk. He isn't helping his reputation here at all.
The dude has an amazing ability to design better
vehicles. His electric cars and reusable rockets are amazing technical break-throughs. I have little doubt that a hyperloop pod would also function as designed, and that he can make a tunnel boring machine that is faster and more efficient than current machines.
But the thing with tunnels and hyperloop tubes is that these are not vehicles, these are
infrastructure, and he has very little experience dealing with that. The closest he's gotten to developing his own infrastructure is probably the Tesla Supercharger network, which has developed much slower than promised and is still missing key features from the original concept, such as solar panels over the charging stalls or on-site backup batteries.
Wait times at some superchargers is more proof poorly-managed/planned infrastructure; what is the point of having a 39-minute trip time from NYC to DC if you have to wait two hours for it?
His battery-swap station is also an obvious failure; when he gave people the choice of 'fast or free,' they almost unanimously chose 'free'. And that gets to the heart of the hyperloop problem as well: It delivers too much speed but not enough capacity. It will be like the Concorde (Musk's own analogy, BTW), where only the super rich will be able to afford it due to 1) the costs of super-high speed operations and 2) the severe capacity restrictions of moving only
840 passengers per hour and all the subsequent supply-and-demand repercussions that will have. With a maximum capacity this low, no government would feel like it is a worthy use of money compared to other forms of transportation, leaving Musk to build the world's longest tunnel all on his own.
tl;dr, Musk can probably make a working functional hyperloop, and can probably bring down the cost of building tunnels suitable for hyperloop pods. But to actually turn these endeavors into profitable businesses would require him to branch out into areas where he hasn't worked before:
infrastructure. And the reason why infrastructure is so daunting is because it is awash in subsidies and government regulation, enough to stifle the free market from participating. The automotive business (electric and gas-fired cars) is only profitable because the government pays massive subsidies for the roads these cars drive on. Airlines are only profitable because the public pays massive subsidies to build airports and keep the FAA and air-traffic control in operation. If Hyperloop is going to be profitable, Musk will have to get a government to subsidize the infrastructure aspect of it, and in the case of Hyperloop we're talking about the most expensive type of infrastructure there is,
tunnels. Combine this with the low capacity of the hyperloop system, and you've got a system that is going for all the wrong records - most expensive cost-per-passenger-mile of any transportation system.
Don't get me wrong, I love the guy and he's earned the respect people give him. I love his rockets and I love his cars - I'm waiting on my own Tesla to arrive. But I hate the way he is able to draw attention (and probably soon money as well) away from worthy transit and high-speed rail projects with his proposals for hyperloops and tunnels that clearly won't solve the problem he claims to be addressing.