And just how do you hope to do that without knowing what a bitcoin will be worth?
Its not a chicken and egg problem, its quite obvious that mining difficulty follows price and not the opposite. Its quite obvious that mining equipment is priced at a point that chases mining profitability. Why else do january orders cost half as much as december orders?
If you like regression theory so much, what do you think would happen when we are hit with a 51% attack, making the mining of new bitcoins impossible? Your mining cost will shoot to infitinty, but do you think the price would follow? OR would it crash ? What if Bitfury were to deploy a 100PH private farm tomorrow? Mining cost for everyone else would explode, would it cause an increase of bitcoin price? And what happens if bitfury decides to double it from 100 to 200PH ? THey double their costs and what else changes? Nothing.
Similarly, if SHA256 would be hacked causing the price to crash to nearly zero, dont you think that will have an impact on the price of mining equipment? Or do you think mining equipment will drop in price first and only when mining becomes cheap, the price of bitcoin will follow?
Miners control only a very small amount of the coins traded each day. Something like 1%. How you think they control the price is beyond me.