Timing is also helping Tesla. With tax credits expiring, pulling some demand in the US forward and starving regions or outside the US over the last half of 2018. Starting Jan 1, the tax credits are still there just a bit smaller and pent up demand in Europe should ease the China pain. By mid 2019, either the tariffs are solved and/or Tesla releases 120D on 2170 with refined interior and HUD. Tesla had always been supply constrained with S/X and they gave always shifted deliveries to where it made the most sense.
Tesla could come out with a P120D using the old form factor cells. The chemistry inside the cells can be upgraded while continuing to use the existing form factor and manufacturing lines for it. This preserves the 10gwh yearly production until they are not constrained on manufacturing. I expect them to be constrained through all of 2019 even with new lines added to GF1. Heck, they will be constrained in 2020 if they actually start building semis even with many new lines at GF1.