I'd love to see a usable intercity passenger rail system of any kind. We could build out a low speed network for a fraction of the HSR cost and then up the speed on routes where it makes sense on a piecemeal basis.
High speed rail makes sense on the coasts. Making a train from New York City to Boston is a good idea (guess what, we have one, and it is the only Amtrak route that is profitable). However a high speed train from New York to LA would be a trip far too long for people to willingly take.
The point is don't try to make a solution fit all needs. Rail in the US is the best in the world in large part because it doesn't deal with humans. This allows efficiency that you can't get when dealing with people. (people don't like sitting in a siding for an hour waiting for an oncoming trail so you have to build more track...)
People will probably end up "packed like sardines" on HSR as well, as HSR will inevitably have to be made to be economical.
Other countries that deal with terrorism operate train systems without people groping your privates. Yet another problem with airplanes is a tiny bomb can cause explosive decompression. That's not a worry with trains - you're not going to kill 300 people with a bomb you can hide in your underwear.
We have the TSA because people are afraid, and we don't travel by plane enough to care.
Because in places where HSR does currently exist, there are no significant security lines.
Trains have fundamental safety advantages compared to planes, so the payoff of an attack is less.
It would be like building four lane arterial road through your city and thinking you could just "up the speed" later on and suddenly have an interchange-access highway.
You might as well bury dark fiber somewhere in there, no matter what else you do. Use one strand for signaling, and lease the rest to backhauler telecoms.