Huge SpaceX fan here, but I've heard from various news sources that the company is famous for aggressively posting dates and then slowly letting them slide. Might that be the case here? (Still, even if it's 2 or 3 years, wow!)
The main factor supporting their claim is that they have a very strong incentive to be ferrying crew to/from the ISS around this time, so barring any big mishaps with Falcon Heavy (supposed to be ready this summer/fall), all the pieces should be in place if not by next year, then certainly just a year or two later. Which, as you mentioned, is just as impressive!
"...The draft report from the GAO, which is Congress’ investigative arm, also concluded that neither SpaceX nor the Boeing Co. is likely to conduct regular space taxi flights to the space station by 2018..."
Shotwell's response is in the best interests of her company, but SpaceX is (as well as Boeing) woefully behind on a reasonable timeline to reach human-rated flight for both their rocket and crew module.
We should have learned from both the early Apollo program, and the Shuttle failures, that human lives shouldn't be treated as expendable capital in this industry.
Both SpaceX's current announcement, and the US Gov's desire to put humans on the first flight SLS flight, are deeply troubling in that regard.
