A high speed train like the ones they've had in Europe for a long time? You know, the ones that regularly reach 300 km/h? If that's not fast or flashy enough for you, what about Maglev? It actually exists, and the tracks are extremely expensive even though they don't even have to maintain low air pressure
I don't see what the US political inability to build infrastructure has to do with my comment. Plenty of countries are still building highspeed trains and iterating on that model... and plenty of non-US countries are looking into hyperloop, the first ones to adopt it will likely be outside of the US, as that's where most innovation is these days. And regardless there's always plenty of room for new ideas.
Unless you think these billionaires should be backing American transportation mega-projects instead? There's plenty of roadblocks there outside of access to capital, where a highspeed train will likely cost 2-3x the initial projections, even if a private company does it. Not to mention the US is a car-heavy market. It seems like a risky project for any non-government entity to take on as it will be packed full of political risk and direct involvement either way...
The US rarely builds major projects anymore except in the defense industry. And almost every major defense project of comparable size ends up being billions over budget or cancelled.