When EM talked about demand, he did not tie it up with their current production capacity, like "ok, the min demand is 500k and we can do that and if it's good times and demand is 700-800k, then we can do that too"
The number of 50% growth is tied to the average for 2018 and we know profitability in Q1-Q2 2018 was not the best.
So, if we compare guided numbers to Q4, then there's not much growth in production and potential costs improvements compared to Q4 ER that stem from "economies of scale". I guess they'll come from other improvements.
It is probably a good approach to set the bar low and "beat", rather than "miss" guidance.
On the other hand, we may see it right in Q1 - if they beat 90k by a large number, then the guidance was too pessimistic and probably shoud not be relied on for the rest of the year.
However, if they are close to the guidance number, then they may have other reasons for containing the growth - whether that's related to costs cutting and not being ready to scale until that is done or being constrained by some bottleneck(s).
Another reason for moderation is a pretty firm statement that they target 7k/week for the EOY.
If they did 7k average for the year, that'd be 336k 3s. With S/X having larger batteries and being cell constrained prob some 70k max. So, very close to 400k total.
If you expect them to beat that and have a lot of upside, they need to be at 7k+/week average.
But then how do you explain this from the letter?
If we assume less than 7k average, for example 6k average, then we get 360k.
So, to me the guidance looks like they'll be doing 6k/week for the most of the year and then do a EOY rush reaching/exceeding 7k.
I guess another variable is GF3. It may be able to add few 10s of Ks by EOY.