The Hyperloop is getting closer and closer to becoming reality, but if it is still not coming fast enough for you (aka Physics Girl) has a decent placeholder for you. It can't carry passengers, just batteries with magnets attached; it isn't sealed off in a near-vacuum; and its max speed looks to be about 7 to 8 mph, but hey, it's a start.
It's fantastically DIY, to the extent that Cowern can make it on her bed. This would be a great project to show a young kid the power of magnets and motion. Watch for the train, stick around for the quick lesson in electromagnetic physics.