Edit: I misread your dates when I first wrote this. What I wrote below is as of at least the Q2 2017 earnings call, and I thought it had been the plan all along, but maybe they described it differently in 2016.
My recollection is that the initially-ordered equipment was going to take them to 5k/week, at which point there would be additional Capex to effectively duplicate the production line to get 10k/week. I expect some of the initial 5k/week CapEx included a lot of stuff that would contribute towards the 10k/week too, as some sections of the line (e.g. paint shop) were supposed to be rated for the the full rate, if I remember correctly. Then maybe some of the 10k/week CapEx ended up being needed to get even to 5k/week (I'm not sure), as they ended up requiring multiple lines even for that. Having said that, it was of course intended to be a fast ramp even in mid-2017, with both stages supposedly happening during 2018.