Isn't this a Boston Big Dig scale project? How will the exhaust fumes be vented? What about earth quakes? Seems to me this requires a year of planning and out just don't start digging next month as he tweeted.
Its quite clear that you don't just tell the public something the moment you start planning it. It's not as if apple announce a fancy new bit of tech then invent them.
He clearly has been planning it for a while.
I will miss Elon Musk when he becomes the president of Mars.
I hope he meets Benny there who has 4 or 5 kids. And two jobs.