There are quantum resistant cryptographic algorithms. Blockchain protocols will be upgraded when necessary.
How can you know when is the time to "upgrade" protocols?
If such a quantum machine will ever be build, it will be a BIG secret for many many years, if not decades.
The greatest advantage of owning a machine capable of breaking crypto comes from no-one else knowing about it. So that everyone is using crypto, that they can break.
If it was public, it would soon be of no use.
Just look what happened with Enigma. After the war England even recommended some countries to use it, because it was unbreakable...
I completely agree with you. It often happens that someone who has some secret wants to use the power of this secret as long as possible in order to be able to covertly affect the situation. There have already been many examples in history when this happened.
