To the generations that traveled the world on boats, constructing flying machines that move faster (and required more tech/maintenance) also probably seemed like an unknown of whether it would be prohibitively expensive or not. I'm grateful that they didn't wait long to explore the possibility, which is what Virgin is doing here.
Maybe I'm communicating poorly here but the tech is not the problem. We don't need to invent anything new, we know how to do it. It does need to get cheaper but the construction and maintenance costs are gigantic and that hasn't changed for any big project over the last century.
Jetliners are complex machines but it's the entire infrastructure of airports and traffic control that actually make it possible, which is only viable because people choose to pay for it. Massive infrastructure does not build or take care of itself, and if it did, that would be a far bigger revolution than just building a train.
