The more I read about this subject the more fascinating it gets. Thank you for the link, although the Op-Ed seems to be dated in 2013 the essence of the current problem is contained within it.
For those have used the same address for multiple payments might be feeling more uncomfortable at this moment in time but in general I guess the underlining fear for crypto users might be that one day they might check their balance only to find their wallet has been emptied and at some stage discover Quantum computing was the tool used for the theft.
What would be the best way for Bitcoin and alts to protect themselves against this threat when it is on the verge of being created?
post-quantum cryptography
like lamport signatures already exists, and it could be implemented into bitcoin today. that's the easy part.
the difficult part is dealing with the 5+ million vulnerable coins (p2pk outputs, outputs sitting in reused addresses, shared xpubs, etc). implementing a post-quantum signature scheme alone doesn't address the fact that 1/3 of the supply is vulnerable to theft. people need to voluntarily move their coins to quantum-safe addresses for the fork to be effective. that could take a few years, based on the adoption rate of segwit.