https://en.bitcoin.it/wiki/Quantum_computing_and_BitcoinIt's not clear whether quantum computers large enough to attack Bitcoin will come into existence in 10 years or 100+ years. If the former, then making Bitcoin quantum-safe in a hurry will be messy, though it can and will be done.
It's certainly not the "end of blockchain technology". Anyone who says that doesn't know what they're talking about. Designing a quantum-safe cryptocurrency is trivial, though it adds significant overhead, which is why nobody's really doing it yet. QRL claims to be a functioning and remarkably efficient quantum-safe cryptocurrency (though still much less efficient than quantum-unsafe cryptocurrencies), but I haven't looked into any aspect of it very much.
A few other coins promote themselves on the bases of being quantum-resistant ( i don't like to use the word "safe" because it's a very inaccurate IMO) .
but you are right in terms of clarity that concerts the the efficiency of quantum computing and it's ability to harm blockchain technology, given the current data we have at our disposal , it's more like a unicorn. but still i see nothing wrong with improving bitcoin if the treat appears.
2. SHA256 isn't vulnerable against QC[1]
"Grover's algorithm makes it a "much easier" to brute force a hash function by using only the square root of evaluations as apposed to current/classical 0/1 computing. while a square root of something may seem like a lot of reduction , but it latterly means nothing when you trying to brute force something which is 256 bits long. "
