If “ocean transparency” comes to pass, it seems much likelier that we’d have to deal with a realignment of the MAD calculus.
One of the reasons countries like the United States and Russia (previously, the USSR) maintain such large nuclear arsenals is to project a credible thread of a second strike - i.e., the idea that any first strike wouldn't be able to completely knock out the opponent's nuclear arsenal. If both sides think that the "submarine" portion of their nuclear triad isn't sufficiently contributing to second strike capability, that'll probably just mean significantly doubling down on ICBMs and forward-deployed bombers (or investing in a different delivery system) so that the calculus remains fundamentally unchanged.
You’re describing an undeterrable actor.
https://nationalinterest.org/blog/reboot/open-secret-israeli...
If the Cold War had turned hot, the Soviet plan was to drive to the Rhine and then negotiate, on the theory that the US might sacrifice West Germany, but that France would definitely retaliate on its own.
Yes, it would violate treaties against the weaponization of space but I would lay even money on the idea that some country has already done this.
It only works as a deterrent if you break the treaty and everyone knows you've broken the treaty (whether you publicly admit it or not) but we aren't there afaik.
It could work if it gets to the point where 'only an idiot' wouldn't have broken the treaty, so you can just assume everyone has, because the idea is fairly obvious, the technology is easy, and there's not any other good options. Or if a rogue state does it or something like it, then you can assume the US and Russia have done it or will be doing it shortly.
at best it's just an "are you feeling lucky?" situation unless you publicly prove it