There is technology for fast rapid mass transit: high-speed rail. Technology was never the issue here. Political will to fund, approve right-of-way, and build it was always the problem, and Musk never even tried to address that part.
In a country with long distances, a well-developed interstate highway system, and a well-developed air transport system. There is a decent rail system in the Northeast and between some other city pairs. But there isn't and shouldn't be the political will to develop rail transport options that don't outcompete those other options especially with electric/autonomous driving becoming an increasing option over the coming…
Acela takes 3h44m from Boston to New York. Not much faster than the scheduled buses (4h15m) and comparable to driving the distance in your own car (3h55m if you stick to the speed limits)