We do need to remember that processing power of quantum computers can increase much more rapidly than we are accustomed to with classical computers.
With each extra bit, a classical computer has more possibilities, but can still only process one at a time.
Processing power of quantum computers may increase more rapidly relative to classical computers but it does not in terms of qbits gained. Quantum computers still need to increase their processing power by a factor of 20-30 before things get interesting.
Did you consider the learning curve and time it will take to train people to program a quantum computer, the time it will take them to code a bitcoin brute-forcer and the time it will take to test it?
I don't think this is an issue. The
algorithm already exists. Whilst a classical computer would take an unimaginably huge 2^128 operations to derive a bitcoin private key, with a QC running Shor this becomes a much more manageable 128^3.
That was my first thought as well, but just because the algorithm already exists doesn't mean it's necessarily easy to implement. I do assume development on implementing Shor's algorithm will start as soon as it's computationally possible though.