[Nyororin]

Willingly allow nuclear weapons? I highly doubt that. Anyone at the top who would suggest it would be committing political suicide, and taking their entire party down with them.

Even with the North Korea issue, they still can`t even get people to approve of defensive attacks off of Japanese soil. Now the defense force is only to directly defend. If there is something outside of Japanese waters attacking Japan (say, a ship or missiles being fired from another country) nothing can be done. There is a lot of push to extend the defense to something more proactive - ie. allowing a missile base outside of Japan to be attacked to defend the country. But even this cannot be pushed through with the large number of people against it.
I cannot even imagine the level of response and backlash a suggestion of allowing nuclear weapons on Japanese soil would bring.