If a country gains this kind of massive economic advantage, it will gain a massive tech advantage as well that, at some point, is likely to allow it to remove the second strike capability. This is more speculative, but we are here talking about the limits of technology and 1-month doubling nanobots etc. Still, this at least should be addressed by the post.
I would go further, and say that if we condition on the US growing to become 70-99% of world GDP and growing super-exponentially for a time, then the fact that it can become a superpower in space pretty much neutralizes MAD, because it’s industry is by and large off-world, meaning that a nuclear attack on the US 50 years after the SIE ended is basically a non-factor, because lots of US people will be in space and able to annihilate North Korea (as an example).
And there’s no nuclear weapons equivalent outside of something like vacuum decay, which is very, very far off from our current state, such that we don’t need to worry about it.
I would go further, and say that if we condition on the US growing to become 70-99% of world GDP and growing super-exponentially for a time, then the fact that it can become a superpower in space pretty much neutralizes MAD, because it’s industry is by and large off-world, meaning that a nuclear attack on the US 50 years after the SIE ended is basically a non-factor, because lots of US people will be in space and able to annihilate North Korea (as an example).
And there’s no nuclear weapons equivalent outside of something like vacuum decay, which is very, very far off from our current state, such that we don’t need to worry about it.