I know it's not a perfect analogy, but with tech gadgets, I'm somewhat of an early adopter, but tend to wait until a measurably more advanced/better model comes out. Case-in-point: I got a first-gen iPad 64GB 3G. Paid full-pop for it. But enjoyed it for quite a while. I kept it until the fifth-generation model came out. I know the iPad 6 is out now, but in my mind, it's not a generation more advanced than the one I have, just incremental improvements. In a similar vein, I held out for the iPhone 5 on Verizon, and only upgraded to the 6 because I was eligible for an upgrade. May wait 'til iPhone 8 comes out.
I've owned my car since spring '11, and currently have about 48,000 miles on it. I figure if I can hold out another 4-5 years, it should still have less than 100,000 miles on it. My premise is that any newer car, when decently maintained, will last that long. So worst-case, if it's 2020 before the Model 3 comes out, my car should still have less than 100k on it. Still might consider an EV in the meantime, but the short range combined with the currently inconsistent public charging infrastructure makes me a little nervous. Most days, my commute is about 25 miles round-trip, but sometimes it's 100. I'd rather have the confidence of being able to make a round trip on one charge, rather than having to hectically try to find a L2 or L3 charger on my lunch hour.