It worries me too. Both model X and S see a tremendous uptake of the 60kWh model meaning overall this battery capacity will make up 50% of their deliveries going forward. Since the discount is $9k on half the cars, that means gross margin will be lower by 4500 per car sold compared to a base case of only the 75/90 availability. With average sales prices approaching 90k, that's a full 5% hit on the gross margin.
However, I don't think we will learn more about this tomorrow. Tesla was very careful not to start delivering any Model S last quarter. You can see this quite clearly in the tracking sheet. I believe this was done on purpose to save Q2 gross margins as much as possible. Note that, with the 'extreme ramp up' troubles, it is very possible that gross margins already took a hit from the a higher than normal number of rejects during April. The latter is a possibility however, not a given.
So the impact of the 60 model will hit in Q3. A lot of posters here are claiming that Tesla had already counted on this and that the refresh simplified production to such a degree that their production costs today are lowered enough to partially or even completely offset the discount. Sure, that is possible, but it is also not a given. And then we must consider things like the Yen getting stronger over the year which likely also has a negative impact on margins.
All in all, margins for sure is a number to watch tomorrow. If they talk them up, expect good news for Q3 (that refresh really bringing average cost down). If they don't really mention them, the other way around.