Boeing is making a long-term play for hypersonic travel

I’m no expert by any means but one major factor is that the airframe is subjected to a lot of heat due to friction which can require exotic or expensive construction materials.

Fuel costs are a lot higher. Concorde used four times as much fuel per passanger as a 747. Plane costs are higher—you need exotic materials and building techniques in the aircraft and engines to deal with the high temperatures. But what really gets you is the economics of building niche products. Even if the long run incremental cost diffefence isn’t that much (say double), only a tiny fraction of people will be willing to pay the premium. That means you might amortize your fixed development costs, which will be much higher of that of a conventional jet, over 1/100 as many planes. 1,500 747s were ever built, but just 20 concordes. The 787 cost $32 billion to develop. Amortizing that over just dozens instead of hundreds or thousands causes per-unit costs to explode.

The engines are likely to be more elaborate than the turbofan you find on a jet liner. To get to Mach 5 you need to accelerate through different speeds and need an engine that works and is efficient enough at each speed. A turbojet works well at lower speeds but cannot go much above Mach 3 in its traditional form. A ramjet is efficient at high mach numbers but does not work at low speeds. One solution is to reconfigure the engine at different speeds, such as a variable cycle engine. Alternatively, some designs include precooling of intake air (sabre), or even a hybrid rocket/jet engine. But all these options are more complex and expensive.

If you remember 1/2 mv^2 = KE from high school physics, then you'll realize just how bad it is. It an N^2 relationship, and that's really expensive. Faster you go the more it costs.

The capacity of those jets will be tiny, even compared to current business class offerings. And they're likely to be more expensive so not everyone who can fly business can fly supersonic.

What will be affected is First Class (which most airlines are already scaling back) but most importantly, private jets. Esp private jet sharing services (e.g. NetJets) will suffer if they can't offer supersonic flights.

Southwest has no first class. All seats are the same. They do just fine and prices are low. They are probably the most profitable airline of all time in the US. That most airlines focus on first class/business class as their money maker means they really don't care much about the rest of the plane. Splitting business from economy might make both better? Who knows until it happens.

It would be interesting to learn how they are going to solve the problems of relatively high apogee orbits. For example, what's going to be done with space junk? If they are going to seriously compete with current airline industry, there are many flights and there are many objects to cross orbits with. Or what about levels of radiation in the middle of ballistic trajectory?

Another question is of reliability at landing - Zarya spacecraft design was shelved in ~1985 because powered landing alone was deemed to risky - and that's for relatively infrequent government flights, not for passenger industry.

The CEO of SpaceX is Musk. Gwynne Shotwell is the COO and President.

Can one make a jet engine fueled by pure hydrogen?

What's wrong with that? Most new technologies come about in that way anyway.

You wouldn't be on the internet today otherwise.