As someone who does this for a living, let me tell you that Elon Musk is a idea guy, not a user. These guys are a dime a dozen and often see things like iPads and flashy technology as "the future", but in implementation, they miss out on things like Ease of User Input, and Long term use strain. A spaceball and a mouse are about the best you can get for 3d space navigation for long periods of time, which is how the people who actually build this stuff use it daily.
You can see this yourself if you want to do a little accuracy experiment. Take your mouse and move it a pixel. Now, take your hand, hold it in the air, and move your hand that same amount without the help of friction on the table or the mouse to rest your hand on. Even if LeapMotion and other 3d space tracking systems were that accurate, it's not an optimal setup for actually doing work, due to strain and other issues. Now, I don't often need single pixel-accuracy, but 4-5 pixel accuracy is needed more often than you think.
Elon Musk sits in a "end item" meeting where the final design is 3d modeled and displayed on a screen, and pictorial representation of that model is manipulated using leap motion. Great. But actual engineering design work done this way? He's dreaming. Or, he's just talking about using Leap Motion et al tied to a CAD program, in which case... Who cares? He's not the first, and he's certainly not a visionary on the subject.