> even if China perfects altering human genetics to create a superior breed of humans, the theory of mutually assured destruction + our arsenal of intercontinental ballistic missiles with nuclear payloads + the concept of a deadman's switch is still pretty solid insurance against anything they can do on a macro level and any other major world power like Russia.

Altering human genetics might lead to a creation of radiation-resistant human. If such mutation gets to a significant percentage of country population, such country might actually welcome an unfolding MAD scenario. (Subject to radiation-resistant food and energy supplies etc)

I think it is ultimately possible - elephants have large bodies but less cancer, cockroaches posses high resistance to radiation, etc. Would this be called "human" is another question...