Extremely minor nit, but it should be point out that Japan is cost efficient because they've mostly built out their "easy" terrain, especially for Tokaido line (the current Tokyo-Osaka line).
The Shin-Hakodate to Sapporo extension will cost them 1.24T yen for 131 km of many tunnels and bridges [0], or US $83M/mi. This cost is why it's taken Japan so long to build a complete Tokyo-Sapporo HSR line, even though the Tokyo-Sapporo air route has been one of the most popular air routes for a long time [1].
They're also working on the Chuo Line which is a new Tokyo-Nagoya-Osaka line going through mountainous terrain that will facilitate 67-minute travel between Tokyo and Osaka. This line will cost 9T yen for 438km [2], which will be a whopping US $187M/mi.
Funnily enough, speaking of the Tokaido line, the president of Japanese National Railway and the chief engineer resigned before its completion due to cost overruns [3]. Japan makes it look easy, but the Shinkansen had a troubled start.
In comparison, for the CA HSR [4], the fairly flat Central California portion is costing $19.5B / 199 mi ($98M/mi) while the more challenging Palmdale-Burbank section is costing $16.8B / 41 mi ($382M/mi).
I know you use it as a figure of speech, but all of this means that a US intercontinental line going through the Rockies would be difficult. Still, I would love to see an intra-Texas, Midwest, or East Coast HSR in my lifetime.
[0] https://www.town.kutchan.hokkaido.jp/town_administration/shi...
[1] https://en.wikipedia.org/wiki/List_of_busiest_passenger_air_...
[2] https://en.wikipedia.org/wiki/Chūō_Shinkansen
[3] https://www.bbc.com/culture/article/20140714-built-for-speed...
[4] https://hsr.ca.gov/about/high-speed-rail-business-plans/2020...