Thanks for putting this together. I'm confident that J/gh will decrease enough to mitigate this, but the possibility that all mining hardware producers fail at making a more efficient miner is highly improbable (especially because there are so many now) but not impossible!
More efficient miners can be made, but at what cost?
For example if it cost a manufacturer $700 to make a 1TH miner at .7watts/gh efficiency today
and it only mines 1 btc lifetime,
how many people would buy it over $840
assuming the manufacturer only wanted to make a 20% markup.
It already seems some farms are shutting down because the miners can not be bought at prices that can justify the cost of the machines versus the bitcoins they can mine in their lifetime, so they are buying coins instead or just stopping the mining and capital investment.