A lot has been said about Model 3 and how it is different from X and such. Here is a different view point.
With Model 3 the complexity is moving from the car to the factory. Musk has said many times that they want to build an incomprehensible "alien dreadnought". Something that is radically different from any other factory that every existed. Nothing off-the-shelf about it. Yet, he also wants to accomplish this, or a working version of it (ver 0.5), by mid-to-late 2017 for Model 3 launch. Every single auto analyst or industry expert said that the new model 3 timeline is unattainable, using the normal way of building auto manufacturing lines. But Musk wants to invent entirely new ways of doing it in that timeline.
From many posts in this thread, from factory visits apparently all we have so far is a big hole in the floor of the factory.
I'm sure Musk will get the dreadnought done. Eventually. Just not anywhere close to the timelines that he has been talking about. If Model 3 is contingent on this, any timeline is just a wild guess, with Musk's timeline being the worst guess (if you disagree with this, you just don't know Musk enough).
tl;dr Yes, Model 3 is simple. But nothing about "the machine that makes the machine" is simple.