There is no past for this type of thing. In 1857, 40,000 people could not sit in the woods of Russia and (potentially, just possibly) ruin worldwide communications, much of commerce, trade and banking, etc, for everyone just by invalidating some mathematics and sending a few letters out stating their findings - with no other direct or indirect manipulation of anything. That's what I meant by saying it's a "public good."
This is unprecedened. I chose $800B as an absurdly large sum that I believe is more than Academia would spend on this question in a few years. (I could be wrong though.)
Downvoter: I know you think it's not secure if a trillion dollars of research can break it - but guess what: there is a nonzero chance that between here and 800 billion dollars from here there is a quantum device. that doesn't mean it actually exists. it means it could exist if one of the world's biggest economies throws that much military R&D at it. I'm saying they shouldn't. at least, not with that goal (breakig crypto for everyone; quantum computing itself is a welcome advance). Please be more practical.