This of course is where BTC resembles a Ponzi scheme. You're right of course it's not technically a Ponzi, but its "inherent value" is based on speculation and greed, which is very similar to a Ponzi, hence the comparisons. BTC is not useful for its original purpose, as a currency to replace those offered by nations and central banks. It's simply too volatile and cumbersome to do this. Hodlers have dropped this pretension and instead now call it a "store of value", which it might become if its price ever stabilizes, if speculators ever get bored and move on. Still, BTC is entirely dependent on the internet and as you point out, extravagant energy expenditures to exist at all, either one of which is vulnerable to disruption. Currently it's also vulnerable to the "new kid on the block", the crypto that actually does what Satoshi envisioned.