Researched it substantially and realized it's an unsolved problem. Anything that makes a dent is incomplete and comes with ugly tradeoffs. For a time I wondered if I should try and solve it myself, but I could never think any solution that hadn't already been/being tried. Years later I'm left curious if it's even possible to solve the problem.
My point is that captcha won't solve this, and solving this problem is a lot harder than it seems at first, and might not even be solvable (which I know is hard to accept).
If someone does find an elegant privacy ensuring way to solve it, I think the impact would extend far beyond HN and could make a big difference to the future of civilization as a whole.
Maybe you are thinking purely from a math / theoretical perspective, but I'm thinking of a compete solution that's practical to use to solve the problem for sites like HN and many others.
We are currently in dire need of ZKP providers / abstractions that will aggregate both eIDs and tradition IDV (scans).
However it's extremely important that the technical capability is there. The next step is to build upon it, and I think that it's a great time for something like this due to all the horrible implementations of identity verifications currently available — that is 3rd party companies collecting scans of documents and biometrics.