First, consider capacity vs. contingency…
Assuming “failure” means a vehicle has to stop mid-trip. (I.e. let’s say, melt-down in the on-board transport system). Assuming we don’t experience RUD (Rapid Unplanned Disassembly) it’s still blocking the tube. (Insert Internet tubes joke here) How crowded is that tube - how many other vehicles? How fast can they stop? How far back to an alternate pathway? (Is there one?) What’s the evacuation process? How long a segment needs to be pressurized to remove the occupants of the stranded vehicle? How far apart are emergency exit hatches? How vandal proof are they? What’s the process if a vehicle experiences a pressure leak during a long voyage?
What if the tube leaks? How easily can it be repaired while not being out of service? How much vaccum pumping would be required to keep pressure low? How do you find leaks while the tube is in use?
Simple physics suggests that the potential speed cannot be realized in an urban area, it takes too long a distance to reach airline speeds unless acceleration is drastic. For inter-city, then we start to look at the issues with building hundreds of miles of tubing. Above ground? underground? Tunnelling vast distances is expensive, and makes repairs expensive. Above ground, why not go with MagLev trains at one tenth the hassle for half the speed and a lot less intrusion on the landscape. Design the track to use smaller trains not unlike the Hyperloop capsules, without the air pressure issues.
Where these options would shine is in the shorter, heavily travelled corridors - SF-LAX-Vegas, the northeast seaboard (Boston to Washington). It’s why trains excel in Europe, and are the volume carrier most efficient for commuters.
All in all, Hyperloop was a neat idea, but the devil is in the details. I see a brighter future for hydrogen-powered aircraft. Inside cities, I suspect the transit of the future is TART - Taxi Area Rapid Transit, where robotaxis can dip into a network of computer-controlled driving downtown tunnels at high speed, emerging onto the regular roadway for the last mile in less densely populated suburbs.