If I'm not mistaken those were ther words of high US official when he met with Xi Jinping recently so I wouldn't count that out from overall equation.
If Chinese think that they can push Japan to it's limits of resources then why Japanese can't think about the same way? Tell me one reason (aside from 'Japan is under US administartion') why they would not do that? What if there's encounter in East China Sea with Chinese aircraft going down above Senkaku Islands? Japan standidng all alone without US backup?
If you're thinking they don't take that as possibility you're wrong. Japan or South Korea ain't no Philippines or Vietnam for that matter. You can't push them around like it's nothing. Take that into account.
I know PRC would hate this move as it would be game changing in the Pacific Ocean.
So after getting nuclear what are they going to do ? Attack China?
When times come to war like Chinese taking over Senkaku Islands there would be no reason for Japan to back down in such circumstances... In conventional attack Japan can't stand up against Chinese superiority in numbers over it's quality without being backed up by the US. What if that wouldn't happen? Changing Japanese constitution would be a laugh when those times would come.