> and intercepting hypersonic vehicles at scale is still tremendously difficult
...as far as you know. Working purely from declassified information, which is all any of us have; but also in clear awareness of the clear forty-year gap between the frontier of declassified military secrets, and what would be the current classified state of the art.
> dead man's switch
I think you missed the part about, uh, the whole other half of how current doctrine works.
Do you know why having cyber supremacy is ranked above having space supremacy?
Because, if you have a sufficiently-good APT, you can have it press buttons! Buttons in places you'll never be able to get a spy inside at the right time! Buttons that subtly break all production missiles at the factory in ways undetectable until launch! Buttons that were meant to give civilian command oversight the emergency-override capability to cancel a pending launch of an insurrectionist military!
(Or, if you don't think that's plausible: "buttons" on a commander's personal cell phone, that calls a staff member of his and deepfakes their voice to tell the staffer to physically hit an air-gapped e-stop button. Add to the theatre by having the APT cut off Milnet-equivalent services at the time, so that a personal cellphone would be the obvious workaround.)
And of course, with previous APTs, you can also steal or more likely, create and plant all the blackmail material you want — to turn previously clean-and-trustworthy "keyholders", into your catspaws, willing to not turn the key when told. (Spies could do this too, but APTs can do it at scale.)
> There's a reason every single nuclear armed state still stands in some form.
Because none of them have yet stepped out of line enough for a major power who has anything "better than nukes" to see the point in showing their hand to their own much stronger opponents who have also moved on to playing this "better than nukes" poker game. (Nobody has had to show their hand at any point in the game so far. It's just been bluffing and folding. Nobody wants to be the first.)
For example, while North Korea has nukes, it has no answer to even basic 1990s-level orbital EMINT; and no functional Navy, let alone long-dive nuclear submarines to serve as untrackable launch platforms. All of NK's nuke launch sites are known — and so could be targeted for bombardment (with plain-old non-nuclear payloads!) in advance of launch, the moment they seem to be getting ready to shoot anyone.
The only reason it hasn't happened already, is that the action of taking the nuke sites out involves cards nobody wants to lay on the table until they have to. It's a move that weakens you, strategically. Although it's something that would almost certainly happen — many times over — the moment a hot war between larger players begins, once all those cards become destined to come out regardless.