We'll eventually find out whether Musk's Hyperloop concept will come to something. It's hard to imagine some of the claims, particularly about costs, will be anything other than underestimates. Just building tunnels to get through mountains north of Los Angeles and maybe other areas will rocket up the costs. I've also been following and peripherally-involved with California High Speed Rail for years, and I know that simply putting your structure up on pylons, which has also been proposed for HSR in places, isn't a guaranteed way to avoid land use conflicts.
Still, for the present, I view Hyperloop as similar to autonomous driving in its effect on our proposed HSR - both concepts have an known unknown chance of making HSR become a huge mistake. Autonomous driving might not be able to go 200 mph, but the cars could pod up together on a dedicated or separated highway lane and drive well over 100 mph. That improved drive time across California combined with the ability to use the time productively because you don't have to drive the vehicle could pull a lot of the market share away from HSR. Or not. Maybe they won't be all that fast or take longer to realize than I imagine.
But if you assigned some number to the risks, like a 15% chance that the Hyperloop will kill HSR before it pays off, 25% chance that driverless cars will do the same, and 30% chance that costs will be so much higher or income revenues lower than anticipated so that it doesn't make sense, that all results in a 55% chance that HSR will be a failure just based on those factors alone. Of course I pulled those risk numbers out of the air but they don't seem unreasonable.
I've been cautiously supportive of California HSR although I don't think it's popular in my area. We need to get people out of planes, soon. Almost everything I hear about it just makes me more hesitant though.
Betting a huge amount of money on a single piece of technology, no matter what it is, strikes me as un-hedged.
Unrestrained criticism of Hyperloop is here, YMMV.