More like a pipe dream with no practical thought put into it that was sold by a conman entirely to derail the planned high speed rail that would have connected SoCal to Seattle.
The end result is a tiny quarter mile tube in a convention centre where you can drive your Tesla in a loop but only like 10 mph and god forbid there's an emergency like a fire because there's no emergency exits if you're stuck behind a burning Tesla.
Actually, maglev trains are slowly becoming practical, and the hyperloop is just a train in a tube with no air. It won't be something revolutionary, just an even faster high speed train. Of course removing air from a tunnel creates its own problems: What if there is a fire? Normally you could get out into the tunnel, can't do that with no air.
It is much harder for fire to exist without air. There are some self oxidizing fires, but it should be relatively easy to avoid those materials. For fires inside the vehicle, there are some existing fire protection protocols that could be followed. There have been fires on the International Space Station and they couldn't exactly run outside either.
The ISS isn't exactly mass transit. In most of those fires, they could evacuate to another area if necessary. That doesn't work for a train where basically all the space is announced for.
Having multiple, semisolated compartments in a Hyperloop train is entirely reasonable. There's definitely room in a traincar for the occupants of a compartment that's on fire to move to another compartment for emergency purposes.
Evacuation points would be defined every so often (say every few miles) such that the train could come to an emergency stop within one, seal doors on each side and let air in. This would take a few minutes, but so does landing a plane or stopping a high speed train.
Bottom line is that fire safety is, to me at least, an entirely solvable problem. The biggest problem with Hyperloop, I think, is that given the materials for the vacuum sealed tube and the energy required to hold that vacuum, it is just so unlikely to be more efficient than a maglev. For medium distance travel, even standard high speed rail is good enough to replace planes, so we don't need the extra speed for ~500 mile distances. For longer distances where high speed rail is super slow or impossible, such as across continents and oceans the cost of building the vacuum tube will be so costly that it would take something like a complete ban of non-renewable fuels in aircraft for it to be a consideration. Even then, I think it could end up being cheaper to develop and use renewable fuels for aircraft.