I suspect the RWD Teslas might tank in value a bit once preowned AWD models are plentiful though.
I was thinking of waiting for AWD, but the base 70kWh battery wasn't enough winter range for us, so that put me into an 85kWh at >>$95K new with not too many options.
Meanwhile, my S85 is well spec'd, leather, air suspension, hifi sound, pano sunroof, premium interior (power liftgate). Those options alone put a new AWD 85 at $100K.
Let's say the 2015 AWD 85 is on the used market in two years time, at around $75K.
Let's say I put mine up for $55K in two years time, that is a very big difference in used price, same options, same amount of remaining warranty (as my car has 4 years to go) so I don't see these two cars in the same league.
We're both selling original $100K retail cars, mine has two more years, and lots more km, but same warranty, for $20K less.
That is still a year before the high volume Tesla is on the market, so I still have a pent up market for a freaky fast and cool luxury electric cruiser, with no cheaper or more compelling competition.
I'm not worried anyway, this won't be my last Tesla. Entirely possible I trade up in 3 years, selling with warranty still on my car to a happy buyer who gets a car that will accelerate every bit as fast and smoothly as the day it left the factory, and has up to date gadget/features (as Tesla keeps updating the car).