they have zero need to build a more efficient miner and sell it to the public.

look at hashnest  they still do well with the s-7
so if they build a s-11 it kills the s-7 
the 67% s-7 number is the key to the s-11

when it gets to 90% and they do 1 more power cost drop to 6.5 cents
they will bring on the s-11