Our contract law is built on the foundation of a shared knowledge base between the two people entering into a contract. The law is very clear that withholding material information from someone to induce them to enter into a contract is fraud.
For example if you sell a car that you know has a bent frame because it's been in an accident, but the buyer doesn't ask, and you don't tell, it's still fraud. Or if you know there is a defect in the ignition switch (GM) or gas tank (Ford), or engine management software (VW), etc. Tesla knew they were making these changes when they signed contracts with probably 500-1,000 buyers. Model S doesn't have enough buyers to trigger a class action suit, but when they get to Model 3, they'll need to grow up and start acting responsible; the free ride will be over. In the meantime they are creating a growing number of customers who feel at least slightly wronged by Tesla and will remember that when time comes to purchase the next car. It doesn't matter how nice the car I bought for $100,000 actually is, or how much I enjoy it, it only matters how I feel about the company throughout my ownership experience.