The vacuum is the hard part, not the maglev. You would need to enclose the entire track inside if a vacuum, and that world be ridiculously expensive and practically impossible with current technology. It’s already very expensive to build a tunnel for a train, which is why they are avoided if possible. But this would need to be all tunnel that is air tight, so even more expensive than regular train tunnels.

To put it into perspective, the current largest manmade vacuum chamber is at a NASA research facility in Ohio. It’s a cylinder with a diameter of 100 feet and a height of 122 feet. If this were laid on its side, about 1.5 New York subway cars could fit inside. The largest vacuum ever made can barely fit the vehicle inside, let alone allow it to travel between two different places where the extra speeds would be warranted.