Another thing, is that anyone that punches a hole big enough in the tube basically transforms half of the hyperloop into a bomb. Energy = pressure * volume. That's a lot of energy smashing through a hyperloop capsule. Basically, imagine if 3% of the tube was filled with pipe bombs, but in reverse.
As long as pod moves, there's a constant pressure build-up of air in front of it, to the point that the design includes a compressor to pump air from the front of the pods because passively preventing the buildup by letting it blow through the pod would be insufficient.
So a leak would be a piffling little annoyance in comparison - there'd not be enough volume of air inside the pods to cause a problem compared to the air the compressor on the pod will be actively pumping from the front of the pod to get it out of the way.
That compressor is absent from every single design we've seen right now, The duct for air to go from front to back would also use up a significant amount of cabin space, and the electric-powered multi-stage high compression ratio high-speed compressor would have massive power usage, weight, and cost. Power usage that would have to be palliated via batteries, as the capsule supposedly has no contact with the tube.
Because of this, no full-scale design yet has incorporated a compressor.
The tube would need egress points, interfaces to stations. I think the difficulty of building one tube between stations is like building a 100km long airplane fuselage. But any proposal is little more than "'just' build a tube!"
The difference between what an aircraft fuselage and what the hyperloop tube needs to do actually seem to be quite massive (caution, back of napkin understanding from somebody who is casually interested but by no means an engineer).
The hyperloop is apparently to be pressurised at around 1/1000th of the pressure of the atmosphere (around 0.015psi). An airplane cabin is apparently pressurised to around 11-12 psi and at an altitude of 36,000 feet apparently the atmospheric pressure is about 3.3 psi so actually the plane fuselage only has to manage a pressure difference of about 3.6 times. So it's like building a 100km long airplane fuselage that has to deal with pressure differences that are something like 280 times greater (please excuse/correct me if this is not the relevant comparison) - although you probably claw back a lot of the difference from a generalised perspective of engineering difficulty from not having to put the thing in the air to begin with.
Edit: I suppose it's more like building 100km of space craft cabin, which probably underscores my understanding of the difficulty a bit better.
