I keep hearing more and more news about quantum computation advancements and optimism. Links later if you like. The meme/promise is that quantum computers will render classic encryption algorithms useless and broken, by the sheer ability to brute force keys in seconds as opposed to centuries. Paraphrasing.
Is this a dilemma for today's cryptocurrencies assuming that happens or can we suppose that "ok private blockchain history for this coin is now public (read: "cracked") thanks to those pesky quantum computers, but from now on we secure additional blocks with new quantum algorithms and hardware and it's secure ForRealThisTime."?
What does a fix for that issue look like and is it backwards compatible?