>Shame that a nuclear weapons treaty with limits and an inspections regime is more sci-fi than the technology needed to remotely verify the presence of a warhead

Well articulated. The early history of atomic weapons regulation hinges on precisely the difficulty of independent verification means (as well as judgements on whether or not an adversary would let you into their country without whack-a-mole style circumvention). I still think that verification technology is the main stumbling block. Neutrino detection is what I (and I bet ongoing orograms in the DoE) focus on for this purpose. We need to be able to figure out how to sense neutrinos order of magnitude more effectively than we can currently. Right now it feels like panning for gold silt with sieves as sparse as chicken-wire.