Unless there's a source I have to call BS on this. High spec cars have the biggest margins and cash is needed for the ramp up. It's in everyone's best interest if high spec'd cars are produced first.
What's interesting is that by first catering to those who already own a Tesla - as a show of appreciation for helping them get to the 3 - they're almost guaranteeing high-spec cars. Not all of them, for sure, but a much higher proportion of them compared to those purchased by folks who haven't owned a Tesla before. Smart move, because they avoid the PR hit while still pumping out mostly high-margin cars for the first couple months. And by also catering to their own employees and those on the West Coast first, they keep everything pretty close to them for the first few months which will cut down on delivery times and allow them to catch any issues and fix them a lot faster.