Quantum computers remain highly theoretical and speculative. And even if they existed in a robust form which was controlled by people who want to use them for nefarious purposes, Bitcoin would be one of the last things they attack.

There are a few technical reasons why most modern Bitcoin addresses are already really hard to attack, even with a quantum computer - but more importantly, if you publicly attacked a vulnerable Bitcoin address, everyone would instantly know you have the power to break their encryption, and would upgrade, so you would lose your ability to intercept information. The best option would be to not tell anyone you’ve figured it out and quietly extract as much valuable information as possible.

Furthermore, it would still likely take hundreds of thousands of dollars worth of energy and millions of dollars worth of hardware, and maybe hours or days, to crack a single private key (if you even can). Which means most addresses today would not be profitable to try and steal from, both from a time standpoint and a monetary standpoint.

Big address would quickly send funds to a soft fork address which uses quantum resistant signatures, while small addresses would be relatively safe and could transition at their own discretion.

I’m still really skeptical that quantum computers can ever be practical for solving the problem of elliptical curve cryptography. From my understanding, they work by taking measurements of the state of “QBits”. The problem is that the number of measurements you need to take doesn’t scale linearly with the amount of QBits you add (and it’s really hard to add more QBits)

So if you had enough bits to efficiently break a public key/private key pair, you’d need to make as many state measurements as their are atoms on earth (from my understanding it’s around that magnitude, although I’m way out of my field here)

TLDR: Quantum is not a problem now, it’s not an unsolvable problem in the future, and there’s a decent chance it never materializes in the way its proponents claim it can (fusion anyone?)