Who knows what the future might hold. I don't have the technical knowledge that OP and AverageGlabella clearly have but I can say this.
I think its worth mentioning that we shouldn't not be discrediting @arcmetal as they have demonstrated knowledge I would expect from a seasoned veteran in the quantum mechanic field. Not to assume they aren't of course but its a breath of fresh air as I have been complaining about the state of Bitcoin discussion and serious discussion not being active enough in the past. The two combined are some of the most surprising members of the forum I've come across the amount of effort that goes into their posts I'm unsure why you guys aren't already receiving the attention you deserve. Most of the other threads discussing quantum computers are filled with generic answers such as "It will never happen" and all that bogus.
The reason why I'm concentrating on the operating costs and the logistics of running something capable of breaking algorithms is that even if a quantum computer was theoretically released tomorrow with the required amount of qubits to breach algorithms it would still only limited to a few individuals which might not have any malicious intent meaning it might not even be a threat anyway. Regardless whether this is true or not obviously we would need to be prepared for the worst case scenario which I do believe judging on others comments on this thread we'll be ready with the technology already available at our disposal.
My personal view point is it all of this doesn't really matter in the grand scheme of things. I like to be more literal and straight to the point. We know the potential threat that is quantum computers. We know the the weak point in the technology Bitcoin is currently using and finally we know how to combat that. I know we have spoken about using an address only once but the majority of people will not go into that effort so the easiest and most efficient way of dealing with this while continuing the usability of Bitcoin would be to deploy a quantum resistant algorithm which I can guarantee is being worked on in the background as we speak.