As has been mentioned in MANY OTHER THREADS BEFORE NOW, there won't be an S11 model for quite a while - Bitmain can't design it 'till there's a new semiconductor node available to design it ON, and that's looking like 1.5-2 years away at the soonest - then they will have to fight with the BIG boys like NVidia, Apple, AMD, Samsung, and such to get any foundry time to MAKE any chips they design.
I'm not betting on there being an S11 model 'till 2019 at the soonest.
that is a good thing for the diff, because we can now draw a linear increase since no efficient miners will take place up to 2020
but a bad thing for casual miners that can't have an efficient miner for mini farm mining