Though there is also another factor which limits mining: the availability of hardware. This cost is not negligible in mining profits, and in fact is one of the reasons the idea of miners using excess green power is a myth: mining hardware generally needs to be run close 100% of the time to make a profit.
That's what I meant when I wrote, mining may be limited by another resource limit. I dread a future, where technological progression is halted or slowed, because people need to dig into landfills searching for rare elements bound to overproduced electronics.
Look at all the compute thrown at heat generation instead of solving protein folding problems for all of humanity. What could be done with terawatts of electrical energy?
I think prolonging the usage of Bitcoin isn't stupid, but downright offensive. Your freedom ends, where my future begins.
It's woefully inefficient, and worse the incentive structure doesn't intrinsically actually align with what's needed to keep the network safe from double-spend attacks. At the moment the income from block rewards from mining (combined with bitcoin's price) is entirely what's driving the energy usage of bitcoin, while what's actually needed is enough proof of work done that a double-spend attack is unprofitable. There's no intrinsic reason these two values are linked: at the moment the energy usage is extremely high, probably far higher than what is needed to secure the network against an attack, but when block rewards decrease in the future, the energy miners are incensivised to spend to get the block rewards will inevitably sink below the level needed to protect the network. The only saviour would be if transaction fees can cover this, but even now with transaction fees being almost irrelevant (<10%) of the miner's incentive, the transaction fees are untenably high for any use as a currency. They would need to rise to $140 or so to break even. This makes the idea of bitcoin as a cheap 'store of value' extremely questionable in the long run, since it is a store of value which requires a constant maintenance by the expendature of energy, which only grows as the value stored in it increases (while an adversary only needs to expend the necesary energy once to pull off an attack). The only way bitcoin could sustain a healthy level of proof of work would be to continuously provide enough value as a transaction medium to justify the cost, and with the current bitcoin that isn't going to work, while at the same time it has basically become fossilised with extreme resistance to any change to the protocol which would provide this.
I think there's a lot of potential value in cryptocurrenies as a concept, and if etherium manages to successfully transition to proof of stake I think it could be in a position to provide that at a reasonable cost, but bitcoin is not it and the position it occupies both crowds out better ideas in the cryptocurrency space as well as being net negative value to humanity as a whole (though it certainly is making some individuals and organisations rich).