"1970: Superconducting trains to go from New York to LA in 20 minutes!"

50+ years later the US has how many high speed trains, of any kind?

Well, Shanghai has some, Japan is building some, and if this discovery is real, Germany might as well revive their Transrapid project (which built the shanghai one).

I guess that's partially missing the point. The main benefit of a superconducting maglev is that it's cheaper to build than a on-rails high-speed train. Specially on problematic terrain (what I understand includes every possible East/West route on the US).

Why would it be cheaper? The actual rails is a pretty small part of constructing high speed rail, isn't it? Especially on problematic terrain.

Because maglev trains can make stronger curves and climb steeper hills.

Energy usage and passenger bandwidth could be a reason