The hard part about infrastructure is getting it through cluttered urban environments, like the Peninsula or LA County. The advantage of HSR is that it can use existing tracks to serve San Francisco and Los Angeles before new, more rapid tracks get build. The trains WILL go from LA to SF, even though they won't be high speed all the way at first. Hyperloop can't use existing tracks and in the first draft Hyperloop service was actually linking the outskirts of LA with the outskirts of SF, NOT LA to SF.
Building things through the Central Valley is costly, but not nearly as much as in urban environments. The first draft of Hyperloop was presented as cheaper than HSR because it didn't account for land cost. Land cost is what accounts for the bulk of HSR cost. Yes, Hyperloop could be built as a viaduct, but so could HSR, and would still have to splurge mney into buying land/indemnize landowners. HSR doesn't have a technology problem as much as it has a land cost problem. And Hyperloop won't solve that.
The original hyperloop proposal called for the tube to be in the median between the northgoing and southgoing sections of I-5. That's how the 6B$ estimate conveniently avoided land cost.
Yes, that works in the Central Valley, where it is already relatively easy to build HSR. It doesn't in urba areas. The constraint on the profile of the infrastructure, both horizontal and vertical, in a function of the speed. In the end what you need in an infrastructure with the right profile, and that is where the bulk of the cost is, not in the system that runs on it.
I'm ready to be convinced that the Hyperloop system is cheaper than HSR, but the problem is building the right of way. Viaduct is not a magical answer, we could have a HSR viaduct with soundproof walls. Peninsula NIMBYs successfully killed building new tracks for HSR, where Caltrain already runs (with almost no additional nuisance). Somehow, I don't imagine them (or any californias suburban community) being OK with a viaduct going through their towns. A viaduct that couldn't be laid on top of existing roads to have the right profile for high speed.
There are very few existing roads that are compatible in profile with high speed. And they are located where the right of way is already cheap.
Solving the right of way problem sounds maybe less sexy than supersonic travel, but this is where we can gain the most efficiency. I think this is a harder problem than the hypersonic technology.
Building things through the Central Valley is costly, but not nearly as much as in urban environments. The first draft of Hyperloop was presented as cheaper than HSR because it didn't account for land cost. Land cost is what accounts for the bulk of HSR cost. Yes, Hyperloop could be built as a viaduct, but so could HSR, and would still have to splurge mney into buying land/indemnize landowners. HSR doesn't have a technology problem as much as it has a land cost problem. And Hyperloop won't solve that.
edit:typos