Might be weather. That pushes it to at least Friday.
[Wednesday-evening update]
Yes, as noted in comments, apparently the launch is back on for tomorrow morning. Elon must have really wanted to do it on 4/20.
[Bumped]
[Late-evening update]
[Thursday-morning update]
Well, the excitement happened. It will be interesting to see the post mortem, but just getting off the pad and through max-Q were major milestones for the first flight of such a beast.
[Afternoon update]
Here‘s Eric Berger’s take.
And more thoughts from Blake Powers.
Marina Koren’s story on Elon’s explosive day.