Migration complexity side is also not straightforward. Cryptographic primitives tend to be deeply embedded in ways that are not always easy to find. FWIW, we built a free scanning tool for developers to find and remediate cryptographic vulnerabilities in their repos (still in beta: https://app.threatpoint.com).
2029 might be conservative or optimistic depending on which variable moves first.
Of course such a model cannot predict a fundamental breakthrough nor can it predict whether there is some kind of fundamental limit to the size of such a quantum system before we have coherence collapse. This is an interesting question for quantum mechanics however.
In summary, quantum computing feels analogous to fusion, a technology that’s always 20 years away.
Oh and don’t get me started on AGI. Lol.
I wonder what a quantum backdoor would look like.