I don't think that's a given. You're assuming that interest in mining will continue to grow at the same exponentially increasing rate forever, but that would m

I don't think that's a given. You're assuming that interest in mining will continue to grow at the same exponentially increasing rate forever, but that would most likely require the price to continue rising forever too. I don't think either of those scenarios sounds at all realistic. The bubble will eventually burst, but the blockchain will continue on. Bitcoin price can drop to $1000 tomorrow and many miners will lose interest on the following day, but the difficulty is what governs how much work is required to put a block onto the end of the chain; not the number of transactions. When the difficulty drops, (yeah it will bring some miners back). In this way, it is extremely beneficial that the price drops for the viability of the network. And sure, that is scary for speculators who may or may not understand it, but this isn't a frozen banana stand, it is a brand new monetary system. There is tons of risk involved for stakeholders. As solutions are implemented that make it easier to include more transactions in a single block, or to safely defer publishing the transactions into a block at all until some later date when there is less friction (SegWit does this?) the number of transactions that Bitcoin may process per second will rise, but the difficulty/hashrate are not a factor in this calculation. The price of bitcoin is what has driven the interest in mining, and the explosion of difficulty is what follows from that based on how the protocol is designed to work. These variables are not in any way dependent on transaction volume by number or complexity of transactions, though. You can absolutely increase or decrease the throughput of transactions handled by the network without necessarily having any dependent effect on energy usage, hashrate, or difficulty. (We could have a fine blockchain with only 5-10 people doing the mining, and it would almost certainly be able to handle just as many transactions, but there are quite a lot more people interested than that.)