First, let's drop the hype, this idea is ancient for 'new ideas', it was published in an issue of Popular Mechanics older than Elon Musk (40s era issue I believe) .
Now here's a huge issue I haven't seen anyone talking about that gets progressively worse as the track/tube length increases, subsidence and ground movement.
Yes, that's right, all those super tight tolerances needed to keep it air tight and within safe turning range of a high speed capsule are at risk.
No matter how much we like to pretend, the earth isn't 'rock solid steady'.
If you don't know what I'm talking about, look up soil subsidence, faults, and even earth tide.
Earth tide is an interesting one and it can be around half a meter, depending on location and conditions, but it effects pretty much the entire planet.
The point is, there are serious issues about trying to keep an airtight low pressure tube of extraordinary length intact and functionally safe, especially when you're going to be shooting giant passenger carrying bullets down it. That's one target you better not miss.
Yes, there are probably a ton of other issues I've never thought of, but I'm not an engineer and it's not my job to be intimately familiar with variant thermal expansion rates or whatever else might go wrong with this concept. I still think it makes cool mad science fiction, but I don't see it being a rational expenditure of resources and effort at this time. (By the way, how much material would such a full sized tube use up, and whats the current national production of said materials?)