This is not likely to happen anytime soon, at least not in the way you're imagining. It could technically be done but it wouldn't be ideal. Car buying is a complicated process.. you have to consider trade-ins (which requires physical inspection), lease agreements and financing, etc. It's not something so simple that you can just click through a few options and be done with it. Even they could simplify it to an online ordering system, it would probably benefit the seller way more than the buyer since you lose your ability to properly negotiate. This isn't something you should hope for.

I've bought a lot of brand new cars.. 3 since 2010 alone. It's a long process for a reason, there are a lot of steps involved and the consumer gets screwed if they can't negotiate.