Not practical in the same space. What train or flight plans will you be canceling in favor of cycling?
...sure. But also, once you build a 5+ million person metro area you're pretty committed to it...
NYC, LA, Chicago, Dallas, Houston, Washington DC, Miami, Philadelphia, and Atlanta.
You could profitably run high-speed rail between NYC and DC, hitting Philadelphia on the way. Amtrak does run a sort of high speed service on this route.
There's a study underway for a privately funded high-speed rail connecting Dallas and Houston.
Miami to Atlanta is at the edge of what might make sense.
Sizable metro areas can decline, Detroit is now 1/3 the size that it was at its peak in the 1960s. The railway station was abandoned.