Other car makers should do this
Ford - "we have this amazing car, plonk down $1000 and we might deliver something approximating our promises in two or three years. Oh and check out the headline price because chances are your car will cost a lot more than that when you throw in the extras. Oh and you might want to read our twitter feed since we have tendency of mentioning extra delays in offhand ways."
Fools with money they wish to part with - "this sounds like a fabulous idea, where do I preorder?"
Sounds absurd but this is Tesla's pitch. I'm sure the Model 3 will be a good car. It may even break electric vehicles into the mainstream. But it's not some limited edition Bugatti or something. They'll make as many of these cars as they can sell. I see no reason that I should give them cash for a car which doesn't exist, won't exist for several years, and may suffer early build or production issues like delays for that privilege.