Unlike most people on this list, I am in the chip biz.  I cannot say much.  I can say this:  A US$300M investment in a 7nm-based chip design will get you pretty much that.  Then you'll need more money to get your chips fabbed and you systems built and installed and everything else.  A few $millions will go a long way towards physical plant for installation, but it takes a lot of money to play in the 7nm game. 

There were some comments in this thread about the move from 22/20nm to 16nm.  The 20nm node was largely skipped by the industry because 16nm node added so much value with the introduction of finFETs, that it wasn't worth it to continue investing in 20nm.  The 16nm node still has a ways to go, and has had a number of rounds of refinements.  I don't know which actual 16nm process is being used by BMT, but they could probably get some mileage just by re-spinning into a newer 16nm process.  If they cared about improving the product.  However they're in a situation where they can sell all they can make, and price is hardly an object right now, so why waste the engineering resources? 

7nm is a huge wall to climb for anyone, and I don't think anyone's going to be building a 7nm miner for at least another year, maybe 2. 

If someone does come along and proves me wrong, I'll buy it.