Exactly, which is why I think the solution is to focus exclusively on the cities to start - make living, working, and spending time there more desirable, functional, and affordable without cars, and I think you’ll start to see the changes radiate out from there. I live 30 miles from Boston, but I rarely go because it’s a pain in the ass to get there. With the current commute situation, the city might as well be on the moon for how accessible it is. If it was fast and easy for me to get to the city I would absolutely spend more time there, especially if they opened up a lot of the roadways for more attractions and walkable space. If I could get to any point in the city within 45 mins, I would probably look into working there as well. But if you took away my main mode of transportation before installing those things as a replacement first, I would just be screwed.
You’re right that it probably will require federal intervention - use the Eisenhower interstate system plan as a guide for high speed rail travel. The bottom line is that you’ll need to put better options in front of people before you start taking things away, otherwise you’ll end up with huge swaths of people forced into extreme poverty and death. If you’re going to bulldoze suburbs for trains, the people living there need a place to go first. Ideally a place they choose to go willingly rather than be forced out because many will end up on the street.