But these are just technological issues comparable to other mundane ones; just like how 3D printing could make it easy to create weapons, or how the rise of the automobile has created an enormous new cause of death and injury. There's not reason to think it would be outside the scope of ordinary policy-making methods to handle them.
Also, Solving Captchas is already pretty damn easy. A combination of algorithmic methods and crowdsourcing makes it quite cheap, especially for sites using older/easier captcha versions. Captcha is not a security plan; it's a speedbump that's getting easier to pass all the time (but still, no crisis will result from this).
Elon Musk submitted a comment to edge.org a day or so ago, on this article. It was later removed.
Now Elon has been making noises about AI safety lately in general, including for example mentioning Bostrom's Superintelligence on twitter. But this is the first time that I know of that he's come up with his own predictions of the timeframes involved, and I think his are rather quite soon compared to most.
We can compare this to MIRI's post in May this year, When Will AI Be Created, which illustrates that it seems reasonable to think of AI as being further away, but also that there is a lot of uncertainty on the issue.
Of course, "something seriously dangerous" might not refer to full blown superintelligent uFAI - there's plenty of space for disasters of magnitude in between the range of the 2010 flash crash and clippy turning the universe into paperclips to occur.
In any case, it's true that Musk has more "direct exposure" to those on the frontier of AGI research than your average person, and it's also true that he has an audience, so I think there is some interest to be found in his comments here.