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.
20 to 30x is only an extra 4 or 5 qubits, though (2^4=16, 2^5=32).
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.
Yes, you're right. I concede the point.
I suppose what I'm trying to say is that it's very difficult to estimate when a QC that is capable of cracking bitcoin might become available, and that we can't use the development history of classical computers as a guideline. The challenges to building a workable, reliable large-scale QC do remain immense, but we are all aware that work is continuing at pace, and a QC threat to bitcoin may be with us soon than we might envisage. I do think it's important that making bitcoin quantum-safe be considered as a problem to resolve
now, rather than at some indefinite point in the future.