In the same conference call[1] Musk mentions that the Model 3 factory, aka Alien Dreadnought v1.0 (their internal name for "the machine that builds the machine") will be fully automated, running more like a high speed bottling plant or an automated pick-and-place machine than a traditional car factory.

Their stated rationale is that as soon as humans are involved with the actual assembly, it has to slow down to human speeds. There will still be plenty of people working in the factory, they'll just be maintaining on the machines, doing continuous improvement, dealing with anomalies, etc.

[1] http://ir.tesla.com/eventdetail.cfm?EventID=174610