Here's why this doesn't work:
Demand Exceeds Supply
Imagine the apple demand was 20 per day - well above the supply of 10. In no time the apple wait would become so long that buyers would lose interest. When the wait stretched out to a few weeks many people would stop ordering apples and the demand would drop until it reached 10, stabilizing the wait at whatever amount of time it took to create a strong enough disincentive. Here it would appear that demand equals supply at 10 apples and there's no justification for purchasing a second apple tree, but it's only because the demand has been reduced by the disincentive of the wait time. Instead of allowing wait times to grow, the apple seller could have raised the price as a disincentive instead. Both reduce demand but with the latter the seller makes more money. Do we see Tesla doing this? Yeah they just raised the price a few weeks ago. In the longer term the better solution is to purchase a second tree. Is Tesla doing this? For sure for the Model 3 and X, and sort of for the S.
Supply Exceeds Demand
Imagine apple demand was only 5. Supply would start piling up. This would expose more potential customers to the opportunity to buy an apple and simultaneously the vendor would probably lower the price to incentivize apple sales. Via some way or another, the vendor would probably find a way to sell 10 per day, (aka making demand rise to 10). Is Tesla doing this? Yeah, with their referral program and adding showrooms.
So just the raw fact that the vendor is selling their 10 apples (or Tesla is their selling cars with stable wait times) doesn't really tell us much about actual demand. Demand is an elastic thing shaped by incentives and disincentives. Right now we see obvious disincentives for the Model S (waits, price increase) and Model X (wait, low initial build quality). As these are reduced, or as Tesla adds incentives (more features, discounts) or as more people becomes aware of the product (advertising) the demand rises. How much higher it could rise is anyone's guess, but the Model 3 pre-orders show that many many people are interested at a lower price.