I'm aware of the fact that nuclear pulse rockets will violate atmospheric test ban treaties. However I think if some major countries were serious about it then

I'm aware of the fact that nuclear pulse rockets will violate atmospheric test ban treaties. However I think if some major countries were serious about it then an exception for pulse propulsion could have been added to those treaties. (Yes, I understand the potential for abuse but in my mind the upsides and an effective monitoring system far outweigh the risks.)