"As of 2019, the largest general-purpose quantum computers have fewer than 100 qubits, have impractically-high error rates, and can operate only in lab conditions at temperatures near absolute zero. Attacking Bitcoin keys would require around 1500 qubits."
https://en.bitcoin.it/wiki/Quantum_computing_and_Bitcoin

"The system here is a model of our 50-qubit system. We’re not that far away from 160 today."
https://venturebeat.com/2019/07/14/ibm-research-explains-how-quantum-computing-works-and-could-be-the-the-supercomputer-of-the-future/

"Quantum computers will soon outperform classical machines"
"The project is part of the EU’s €1 billion, 10-year Quantum Flagship initiative to kickstart a competitive European industry in quantum technologies."
http://www.engineersjournal.ie/2019/07/01/quantum-computers-will-soon-outperform-classical-machines/

Professor O’Brien: "In less than ten years quantum computers will begin to outperform everyday computers"
“The very fast computing power given by quantum computers has the potential to disrupt traditional businesses and challenge our cyber-security. Businesses need to be ready for a quantum future because it’s coming.”
Quantum computing is coming – are you prepared for it?
http://www.bris.ac.uk/physics/news/2016/quantum-computing.html

Quantum computers are expected to exceed the capabilities of classical computers in the next five to 10 years and promise vast increases in processing power over silicon chips.
https://thenextweb.com/future-of-finance/2019/07/15/quantum-key-distribution-to-secure-bank-account/

Some of Britain’s most distinguished computer scientists have moved to Silicon Valley to produce a quantum computer that can be sold commercially within five years.
https://www.thetimes.co.uk/article/quantum-computing-lures-scientists-to-us-g7kkkkvjw

Accessible quantum computing is just around the corner
https://techhq.com/2019/07/accessible-quantum-computing-is-just-around-the-corner/



Maybe earlier:

Stewart Allen, COO of quantum computing startup IonQ:
“I think in two or three years we’ll have businesses that are using quantum to solve real-world problems,” explained Allen; in the coming years, we can expect to see a trend of early adopters who want to have a “first-mover advantage”.
https://techhq.com/2019/07/accessible-quantum-computing-is-just-around-the-corner/

'Shalecoins' will be moved and are their (the first group) reward. That is the big Bitcoin challenge.

Then we will have a quantum secure network.