Some hypothetical thoughts about price stability, (lack of) price/supply feedback and long run electrical cost.
Not a call to change anything just some thoughts.
One observation people often make about the difference between bitcoin & gold is that gold reacts to price changes, by rate of supply increasing when price is high, and rate of supply decreasing when price is low. This effect has some positive feedback loop in the direction of stabilising gold price. Products with an inelastic supply function (like bitcoin or farming with long production lead times) result in gluts and shortages which take longer to self-correct than something with an elastic supply function.
While bitcoin cant directly know its price as that is an externality, one related thing it does know is the rate of difficulty change. An indication that supply is too high would be that difficulty is slowing, or similarly an indication that supply is too high difficulty increasing too fast.
So we could (hypothetically) change bitcoin to decrease subsidy per block if difficulty increase is above 10% per 2016 block period (2 week retarget). What could we do with the unclaimed subsidy? We could defer it so that bitcoin subsidy lasts for longer, and/or we could bring it forward again if difficulty slowed, eg for example increase the subsidy per block if difficulty increase falls below 0%.
If subsidy is not deferred, just deleted, that saves electricity and reduces the supply.
One might even speculate that the absence of price or rate of difficulty change feedback is currently causing price drops as mining difficulty is falling for the first time while the production cost (mining) is efficient (close to market price of coins) even for the most efficient operators. Or put it another way miners in todays market would be happy to get another 5% at 13.125 btc/block over 12.5 btc/block.
A second question is if bitcoin is $10,000/btc or $100k or $1mil which would be supported by various real-life uses eg see page 5 of report comparing to different aspects of gold ownership
https://cdn.panteracapital.com/wp-content/uploads/Bitcoin-vs-Gold.pdf then at those prices, what happens to electrical use and mining investment. Is the result sustainable.
Now one argument is more security is needed for higher market cap $21 tril? And another argument is you cant have mining cost artificially pulled below market price or people will expend that amount of money anyway to bypass, bribe, hack etc the artificial factor. (eg Paul Sztorc makes that argument in his blog post
http://www.truthcoin.info/blog/pow-and-mining/) I notice Nick Szabo made a similar point in an old blog post also. The cynic may like to think of the lack of mining for USD (or other fiat) leading to huge expended effort for people to lobby, bribe etc to get access to government funds, where those funds partly come from inflation (which is a form of taxation) and also quantitative easing and bailouts. The resources arent actually saved, they they just go into lobbying efforts and create cost via inefficient allocation of capital that arises as a cost of moral hazard.
Maybe at these prices subsidy ends up being too high for the needed security and transaction fees cant go negative! Anyway it would also be possible to voluntarily shrink subsidy per block (phased in over time to respect mining investments).
Adam