It's very interesting that this is a SpaceX project. Why not Tesla, or another company entirely?
[Edit: If anything, this might lead people to take this type of eccentric and radical design more seriously. But given the criticism Musk's engineering ventures have had before, I wouldn't count on it.]
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I wouldn't read into that. Musk has said he has no intention of developing it; he probably just needed a place to put it. SpaceX makes as much sense as anything else.
That being said -- hopefully he lied when he said he had no interest, in order to quell speculation until the announcement. Kind of like how Apple says they'll never ever launch certain things... right up until they do it.
"Feedback would be most welcome – please send to hyper loop@spacex.com or hyperloop@teslamotors.com . I would like to thank my excellent compadres at both companies for their help in putting this together."
- from the pdf