Crypto exists to make early crypto holders money.
You get in on the speculative promise of making yourself wealthy. It's sold to you by the people at the top, and the message is amplified by the grifters and the pick mes in their orbit.
It's never been a convenient exchange of money. If they'd focused on this, maybe the argument would have worked. Instead, it's wacky and has the worst UX of any banking apparatus in the world. Including giant US banks stuck in 2005. This sucks because this is literally the value being sold, and it doesn't deliver on it at all.
By the time quantum chips can attack crypto's underlying hardness (2029?), most of the coins won't have the engineering talent and support left to migrate to more secure cryptography. We'll start seeing shit coins popped left and right, which will cause mass panic. That will cause sell offs, even if the big name brands manage to secure themselves temporarily.
Post quantum cryptography is not fundamentally that hard, the only issues are the signatures are bigger (so the chain is less efficient), and migration of existing chains (biggest problem).
Quantum computers might harm BTC or some other chains if the devs can’t get their house in order soon enough, but there’s no reason to think it fundamentally alters whether cryptocurrency is mathematically viable
Migration for certain prominent projects is already underway, e.g Ethereum.
It's too late.
How are you going to mass migrate all of the cold, dark wallets?
It's not going to happen because it requires conscious, deliberate, careful migration on the part of the wallet owners. You won't even be able to contact or warn most of them, let alone get them to understand the process.
Probably half the value in Ethereum and Bitcoin will be popped this way.