Working backwards from Tesla’s statement that the China gigafactory would build Model 3 AND Model Y next year: you don’t want to do this without trying this out in the USA first:
Meaning Fremont needs to build both 3 and Y:
Fremont is ‘full’, which means some existing production needs to be cut to make space for at least on Model Y line:
Sacrifice the least profitable old product: the 75 S/X. This means you need less than half the production S/X capacity so you can shutdown the oldest S/X production line and keep production on the newest one.
Panasonics contract for Japanese cells ended on 1/1/2019. Replace the battery pack with a battery pack built in the gigafactory. This frees up more production space in Fremont. Not sure if the S/X motors are still built in Fremont, but if they arent’t, move that too to Gigafactory 1k freeing up more space in Fremont. You now have a lot of free space in Fremont, probably enough to build a new Model S/X line with more automation/efficiency than the old one, in less space. While you’re at it, build that new S/X line to build a S/X refresh.
When the new S/X line is ready, eliminate the other S/X line, and build a new line in that space for Model Y.
So its obvious that during this transition period you need less S/X personel, and you still won’t need those after the transition because the new line will be more automated.
So in a year or so would expect Fremont to have 1 new S/X line, current Model 3 lines, and a new Model Y line. Gigafactory would do what it’s best at: building battery packs and motors.
This is all speculation but fits perfectly with what Tesla already has publicly announced recently about GF3 and the layoffs.