There are contrary opinions of course, but here are mine:
We'll see minor updates of both S and X that will have tangible performance and range consequences around 4Q
In roughly 2019 they'll announce completely new S and X for 2020 delivery. They probably will look more or less similar to today and FWD will be there for the X. The redesign will allow major reduction in production cost and increase of production quality. There will be major changes to drivetrain, that will follow lessons learned from Model 3.
I think that will happen even though Model 3 rampup, Model Y, Semi, Pickup, solar roof, conventional PV, storage products, new GF's, expansion to a dozen new countries etc are also happening.
We all know Elon does not want to be bored. I think all of this will soon be largely formulaic because the learning curve has been so steep. Scaling all this, including new models will be easier than growth so far has been.
...and I don't even like Kool-Aid.