You know you are running on crypto time when 60-90 days from now ISN'T the 'near future'. 

Since this is the speculation thread, I would speculate that initial yields on the new 7nm chips will be so low that the machines won't be available in any significant qnties for many months. Not crypto many, but real many. So I would not be too concerned about any sort of big difficulty jump. A couple thousand machines will barely be a rounding error and a lot of them will likely go to replace older gear. The first batch for pre-order will probably get the best chips from the first tape out as well, and will also be the most expensive.