A couple of notes;

if passenger train travel is already uncompetitive on price, faster train infrastructure is considerably more expensive relative to that. I am not sure whether that cost is fundamental or not -- maybe it's possible to find ways to build HSR infrastructure more-cheaply.

Fair, but it’s not like passenger rail is uncompetitive when taking everything into account. Cars are subsidised far more, and both cars and planes have far more negative externalities (i.e. real future costs) than trains. Plus, there’s a very real cost to being dependent on oil states for the bulk of our transportation options, one that has somewhat been demonstrated by the war in Ukraine.

I do agree on your point about high speed rail compared to normal rail, although I do think there is a lot of value in them being top of the line services to make rail as a whole more attractive.

Self-driving vehicles. Some of the objections I've seen to use of sleeper trains -- one way to mitigate the issues of trains being slower than planes is by having travel happen when asleep -- is people who dislike having shared sleeping environments. Maybe it's possible to do, oh, a self-driving car with a sleeper trailer or something like that.

Cars straight up suck and are less efficient than trains. Why you’d think of a car with a caravan but not, idk, private sleeping compartments in trains, is beyond me.