May I add my own bit of speculation (and pure speculation it has to be):
There are 4 Model 3 lines:
GA1 and GA 2 are inside the Fremont factory and did not perform as well as intended, probably limited at 1.5 k per week each
GA3 is inside the Fremont factory and is performing as intended, but still spinning up (to 3K/week?).
GA4 is temporarily located in a tent outside the Fremont factory and just getting started.
When GA4 works at full capacity, they can close GA1 and replace it with a GA3/4 clone.
When this is done, they can close GA2 and GA4 and move GA4 to replace GA2 - and remove the tent or use it for something else.
Then they have GA1, GA2 (former 4) and GA3, probably each running at > 3k per week. Time for this might be end of 2018/early 2019.
Just my guess, but it explains why they put a line in a tent and hopefully fits with the shareholder meeting Information, yesterday´s e-mail and the general talk of 6k/week as an intermediate target.