Bitcoin can't always be proof-of-work. Given the capped supply, the mining rewards will eventually diminish to the point that the network is no longer secure. It will have to transition to proof-of-stake or some other mechanism long before that happens.

It intends to rely on fees, i.e. to have a constant backlog of high fee paying transactions. We'll see how that plays out within a few decades as the block subsidy becomes insignificant.

Transaction volume goes up and down. Just look at ETH gas prices - varying between 1 and 1000 month-to-month. BTC holders aren't going to be OK with a temporary lull in transactions leading to a double-spend attack etc.

I agree it seems wildly optimistic.

We are still waiting for AI (Deep Learning) to do the same and move to efficient alternatives without incinerating the environment and consuming the oceans to cool their GPUs whilst training and doing inference on their AI models.

So many years, yet no practical efficient solutions currently in production to reduce the emissions AI is producing. Much more urgent than crypto since that already has largely moved to proof-of-stake.