I first read about this concept back in the 70s or early 80s as I recall. I suppose if it were a workable idea, it would be a reality by now, or maybe it could have worked, but the development got caught up in red tape. I'm not convinced either way at this point.
At any rate, I recall the system being described as a solution to long-distance, express travel in an evacuated tunnel and a maglev train suspended on superconducting magnets. The first part of the trip would expend the energy accelerating the train to outlandish speeds, and then nearly all the energy would be regenerated by decelerating the train at its destination. Theoretically the top speed would only be limited by the straightness of the "track" and the length of time available to accelerate/decelerate. They discussed a transcontinental train that could be faster than an SST, and much more economical to run. The initial construction cost of course would be preposterous.