Sure, but breakthroughs are unpredictable by nature. And we can't even prove mathematically that our cryptography is secure against classical computers or a guy with a pen and some paper.

000w2

bitcoin

How hard will it be to reach consensus about a quantum upgrade ?

stack_harder

Generally agreed, but look at the progress of quantum computers:
In 2001 the number 15 was factored with Shor's algorithm on a quantum computer.
In 2012 Shor's algorithm was applied on a quantum computer to factor 21.
And now it is the year 2025 and we are still on 21.
In practical cryptography we use numbers that are about quattuorvigintillion times larger.