Well, if you're going to talk about evacuated tubes, you might as well throw in maglev at the same time, because you've just tossed out every bit of existing infrastructure anyway.

When we see room-temp supercondutors and commerically-viable fusion, I reckon maglev (and the power it will demand) will be really viable, because those two will tend to overwhelm the negatives on an overall equation. As it stands, color me skeptical of ignoring the entire legacy infrastructure. It's like saying we have a nifty new automobile that runs on water and goes 200 mph, but you'll have to build an entire separate road system for it that can't work with anything you've ever built before.