Tesla Motors expected to sell on the order of 15,000 Model S per year. The first full calendar year they exceeded that target, reaching around 22,000 Customers. The following year they sold 31,000 Model S. And last year they sold over 50,000. They are expected to sell 60,000 Model S this year. Thus, they will have sold on the order of 11 years worth of Model S in only 4-1/2 years -- for a car with an 8-year product cycle. That is vastly more than Naysayers claimed was possible and is a fact that is constantly ignored, even by Tesla Enthusiasts who claim to be 'realistic' while stating pessimistic 'achievable' goals for the company. Anything and everything that is sold of this version of Model S through June/July 2020 is pure gravy at this point. That car has paid for itself multiple times already. That is why Tesla has no concerns whatsoever of the Model ☰ 'cannibalizing' sales of Model S.
From my perspective, the singular biggest cause of 'delay' for the Model X was the unprecedented success of Model S. The biggest cause of 'delay' for Deliveries to RHD territories is that those buyers were vastly outnumbered by new owners in LHD nations. If Tesla Motors had never progressed beyond ~300 units per week with Model S Production, you would have seen the Model X come to market in 2012 as planned, but it would not have been as good a car as debuted in 2015. If everyone and their Grandmother's Sister Sarah had done as Tesla expected and chosen the Model S 40 on the vast majority of orders instead of the Model S 85, they still might have managed to squeeze out a handful of RWD Model X way back in 2013. But it turned out that instead people wanted to get as much range and performance as possible instead of being frugal and 'saving money' by getting a less expensive car. If Naysayers had been correct and there had been a 'limited market' for 'expensive electric cars' the Model S would not have outsold Porsche Panamera, AUDI A8, and BMW 7-Series going on four calendar years straight in the US. Oh, and the Mercedes-Benz S-Class would have been swept too, but managed to secure the #1 spot in 2014, while Model S claimed #2.
Tesla Motors has already accelerated their plans for Model ☰ Production. When the first Model S Deliveries were made, there were 10,000 outstanding Reservations for it. Six months later, after 2,500 had been Delivered, there were 13,000 outstanding Reservations. By the time the first Model X Deliveries were made over 25,000 Reservations were in place. Elon Musk has stated he and Tesla were surprised by the number of Reservations from the Model ☰ Reveal Part I. So in preparation for an expected onslaught of new Reservations following the Model ☰ Reveal Part II, the Gigafactory will be enlarged to a higher maximum capacity -- three times the original total. Tesla is targeting 2018 to reach 500,000 total units from Fremont. Even if they 'only' reach 60% of that goal, that would be perhaps 100,000 of the Generation II vehicles and 200,000 Model 3. If 60% of those go to US Customers, that would be 120,000 Model ☰ sold in 2018. For comparison, the BMW 3-Series sold about 95,000 units in the US during 2015.
I say all this to point out that the 'history' of Tesla Motors is more than just 'having a late start'. The actual history also includes the fact that no matter their Production targets, interest in their vehicles tends to be higher than expected. I believe the preparations that Tesla is doing ahead of Model ☰ Production are meant to diminish these concerns as best as possible. Thus, predictions of a relative 'handful' of Model ☰ reaching Customers during 2018 goes beyond pessimistic, is nowhere near realistic, and ventures into the realm of the ridiculous -- likely fueled by generous helpings of HaterAde.