Ive said it once, I've said it 36 times. Interconnected regional HSR with schedule coordination from one region to the next is the way forward in the US.
Let's say CA HSR involves SF/LA/SD/Sac/Vegas. That connects to another system with Vegas/Phoenix/SLC, and so on. Just as Texas Central can eventually expand into OKC and MSY just based off of proximity.
First of all the Texas Central isn't compatible with California HSR in things like loading gauge, according to my understanding.
Second, the advantage of high speed rail over air transportation vanish for trip beyond 4 or 5 hours, and trip from American Pacific coast across Rocky Mountain into major Texas cities will take longer than that
I never said it would make air travel vanish, but it would have an impact on regional flying if done correctly. And I'm definitely not saying someone is going to travel from SD to Denver via multiple interconnected rail networks, but it does help connectivity when someone living in Ogden, UT wants to get to Ft. Collins or Pueblo,CO if Ogden is in a different regional system but can connect in SLC or Grand Junction to a system that can take them to COS. Similarly to how you can take the SNCF to Stuttgart then take an ICE train to Zurich, and the like.
I mean the "advant of rail travel" would vanish for longer trip, not that air travel would vanish.
There are still people who would travel on longer HSR routes but they usually stop being the most prominent choice and thus they failed to attract most passengers along the route.
Obviously there will still be demand for the smaller cities in-between but the total quantity of travel demand of such smaller cities will also be less.
European cities are much closer together, that each of their range of 4 hour HSR travel distance can overlap and in turn be foundation of a nation-wide HSR network, it'd be difficult to say the same in the US.
Any hope for short and medium haul high speed rail vanished in the 1970s. Freight lines have always been given preference since Amtrak was founded. And that is a shame. As much as I love the multi-day trips across the country, there would be much more profit in short and medium trips as compared to flying or driving. Many stations are in or near the center of town which is near transit connections. But, we have always been told that rail travel is unreliable and slow so cars and air are the only choices.
When I lived in STS and had appointments in SFO, I would very often drive the El Cerrito BART or the Larkspur Ferry. Even though it is more convenient to have a car, I didn't have to deal with paying outrageous parking fees, fighting traffic in the city, sitting in stopped traffic. Same in PDX and SEA. I have yet to try LAX and SAN rail but those seem about the same.
A number of countries have their existing network too occupied for other uses, hence they create a mew company to build a totally new network of HSR. It doesn't have to depend on existing rail.