It's technically feasible of course but the claims are ridiculous. You obviously can't fly anywhere in the world in 4 hours at mach 2, and the $100 price tag is just stupid, which further solidifies the sentiment that it's just some kind of scammy attempt to gather funds. I bet even a simple calculation for fuel costs and zero profit margins won't give you the $100 promice even on high volume and "short" routes like NY-London.

And people overestimate how much someone's willing to pay in exchange of time. Even if you save 4 hours of flight (which is only a portion of the equation), you'd have to value your free time at least at $50/hour to pay even just $200 more. Some will, most won't. Europe is dominated by low cost airlines so I don't see the market for their product.

>"Either we fail or we change the world,"

Well this isn't a selfie filter, if you fail you kill lots of people.