Demand is high, and developing a new platform makes no sense.
Earlier this year, Tesla CEO Elon Musk stated that the upcoming Tesla Model Y small SUV would ride on its own unique platform. That actually surprised a lot of people because the previously announced plan was that it would share the new Model 3's underpinnings. Wouldn't developing an all-new platform be expensive and time consuming? Yes to both, and now Musk has changed his mind. The real life Iron Man has gone back to the original plan for the Model Y platform, and it will probably go on sale in late 2019 or 2020.
That date could now potentially be pushed forward given that there's no need for an entirely new platform. But don't think Tesla isn't planning to modify the Model 3's platform for SUV duties. Oh, there will be changes but nothing too dramatic for the sake of getting the Model Y to market as soon as possible for SUV crazy buyers. Musk claims Tesla engineers will change the wiring harness architecture in order to ease automation in the production process. That will probably be the most significant change. Originally, Musk wanted the Model Y to ride on its platform because he wanted to ditch the 12-volt battery architecture, which would eliminate the lead-acid battery.
However, top Tesla management convinced him to change his mind, or, as Musk recently told analysts in a conference call, "walked him back from the cliff of insanity." Like the larger and more expensive Model X, the Model Y will likely have those love them or hate them Falcon Wing doors. But one new Tesla at a time. The Model 3 rollout is currently underway, and assuming all goes well there, the Model Y won't be far off.