Would it be possible to have a tunnel like that and somehow fill it with air instead, then accelerate the air to something like 2x the speed of sound outside? That was my first association when he said "there are other ways to store energy than batteries". Then you arrange the whole thing in a loop. You could have some sort of carriage that just gets carried along by the airflow.
Anyway - the part about electric VTOL aircraft got me really excited. I've been annoyed that no one has tried to do VTOL aircraft with fans yet. If it could be made electric too (I'm assuming on-board generators or fuel cells here), that would turn a lot of things on its head.
I was thinking along these lines .. but instead of moving the air, remove it from one side of the train, and then allow atmospheric pressure to force it through the tunnel.
Possible, but not efficient. The drag of the air against the interior of the tube will be really high. Much better is to suck all the air out, and use another drive system (maglev with linear motors).
Anyway - the part about electric VTOL aircraft got me really excited. I've been annoyed that no one has tried to do VTOL aircraft with fans yet. If it could be made electric too (I'm assuming on-board generators or fuel cells here), that would turn a lot of things on its head.