One will be able to assess Tesla's real market performance when the major manufacturers start selling EVs with comparable mileage capabilities.
I would much rather wait to buy an Audi EV SUV or a Mercedes EV SUV in 2019 or 2020, than buy a Tesla Model X right now. By waiting just a year or two, one deals with local dealerships, you have the usual availability of spares and parts for maintenance and body work, plus the already well-known quality and workmanship of an Audi, Mercedes, etc.
Tesla is not a bad choice, but when one is able to choose between a Tesla and Mercedes/Audi/BMW/Ford/Toyota/etc with comparable stats, I think most people will stick with the more familiar brand that they can buy from their local dealership.