If I remember correctly he said it would be feasible for long distance (>1000miles) but fast air travel would probably be more efficient at that point.
"The Hyperloop (or something similar) is, in my opinion, the right solution for the specific case of high traffic city pairs that are less than about 1500 km or 900 miles apart. Around that inflection point, I suspect that supersonic air travel ends up being faster and cheaper"
Found the quote (http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf):
"The Hyperloop (or something similar) is, in my opinion, the right solution for the specific case of high traffic city pairs that are less than about 1500 km or 900 miles apart. Around that inflection point, I suspect that supersonic air travel ends up being faster and cheaper"