There are cities within distances where it would make sense in several regions, but the speeds would be terrible because infrastructure is not up to the task (

There are cities within distances where it would make sense in several regions, but the speeds would be terrible because infrastructure is not up to the task (example: 300 miles in 7 hours 45 minutes). The rails don't support high speed service, there is no electrification, and the rails themselves are owned by freight companies. If the time was productive, you might get some small number of people to take it, but the excruciating slowness wouldn't appeal to many people.