The need for the vacuum is the tricky part of the concept, as you could have a very low drag of the vehicle as long as the air surrounding the train moves as fast as the train, which would be possible in a closed pipeline. Unfortunately you would need to invest the energy to push the whole mass of air inside the tube and accommodate it's friction on the inner diameter as well.
I don't know how much less friction a gas in a solid tube has by reducing it's pressure, as that's some advanced aerodynamics, not solvable by taking the cross sectional area into consideration alone and the length of the tube is undefined so far.
Conventional trains go too slow for this to be significant, high speed trains just use a modified frontal section and probably max out by limitations of the chassis. Their length is very limited compared to the inner diameter of a 1000km tube, therefore I guess air resistance itself is not the big factor to conventional trains. So it either needs 1000km/h and magnetic levitation/very advanced chassis to actually matter or it is a lot of effort for very little gain. At the same time the losses for a Hyperloop are hidden in the pneumatic propulsion system (sled as a piston). Which means the longer the tube, the more losses you get in (gas) friction.
Then the change in temperature by the expanding propulsion-gas (or even just residual gas moving, or condensed water inside condensing) would be a problem in itself to such a structure. That would need some high-tech materials in the assembly, with stable temperature coefficient, high-strength or at least accommodated for it. A slick (steel-) tube wont cut it.
There might be solutions to these problems, the tube would not need to be slick, it could be corrugated or be the bellow frame, the pressure reduction could be a feature within the grooves (like pistons that move outward to reduce the pressure by some amount), it is the unknown length and the additional requirement of reduced internal pressure that increases requirements dramatically. I mean I get into the fallacy of the concept drawing and start using these in my mind before thinking about what they are, just a concept drawing.
Anyway, things figured out or not, all these things (and all not-yet-discovered ones) add up and all speak against breaking even to make a business model that works competitively against conventional trains. If there are advantages, they come from shifting from/to another inefficiency or at the cost of safety.
It is new, it is a great mind-bender, maybe even a great advertisement to involved parties, but kind of hopeless, it represents the search for a new inspirational pie-in-the-sky project.