"Cool" and "new" usually ends up meaning "expensive" and "proprietary" later on, especially if it's not standards conforming and tries to reinvent the wheel.
BART's technology was created by aerospace engineers who wanted to reinvent the railroad and make it "better".
What this resulted in was
- a wider track gauge than any other used in the US
- bespoke rolling stock with different braking, control, coupling systems
- untested ATO that had several early failures
The first two have had lasting impacts; servicing BART equipment is very difficult because no one else has ever made traincars like that, and it makes it difficult to extend BART over existing rail tracks. The expensive of all this "cool" factor is at least a factor of two over standard rail projects, which is why eBART was built as a normal diesel rail line instead of as a BART extension.
Other examples of "cool" transit technologies that ended up aging poorly because of their rarity are monorails and maglevs. With economies of scale it's hard to beat trains, and trains already go to 220+ MPH; there are very few markets where you would need to go significantly faster via land, and where doing so would be a big advantage over air travel, as Hyperloop is proposing.
See: BART