The issue is that people will jump ship especially since the reservation fee is refundable. By 2018-19 other manufacturers will have alternative electric vehicles ready to ship.
It's been years and there is no credible competitor to the Model S. Maybe it will be different with the Model 3, but until an equivalent car is on the road I'm not sure I agree with your statement. The Bolt - a nice car, and I've test driven it - is just so clearly sub-par compared to what Tesla is aiming for with the Model 3 that I would not consider it a true alternative.