It’s really not that difficult to come up with a Torment Nexus that, given enough money, could be built today. I’m not sure why you’re convinced it could not exist. Just browse a bunch of Wikipedia articles about torture and ethnic cleansing and general injustice and connect some dots.

Another point of the Torment Nexus is that it’s dark humor that science fiction writers especially will ideate something in their writing, and spend great lengths discussing the inevitable harm it unleashes, only to wait a few years and watch as someone actually builds the thing they basically warned everyone about. It’s a placeholder for “thing so bad that I don’t actually want to describe it lest some psychopath actually builds it.”