Japan is not going to go nuclear. If they do, very bad things are probably ahead.
(pinging DTogo because maybe he can explain this better than I can)
Japan has already "gone nuclear" in the sense of power generation. Not sure of the need for their own bomb with the US military presence there, and it's a very hot political potato given their experience with The Bomb in WWII.
Bads things ahead? Like Japan using it? Highly unlikely. It's neighbors will exercise mock outrage for their own domestic politics, and trot out Japan's WWII aggression - they do that anyway.
A nuclear Japan is nowhere near the regional threat of N Korea, or an unstable Pakistan infested with Taliban sympathizers. IMHO
日本＊ピング＊ (kono risuto ni hairitai ka detai wo shirasete kudasai : let me know if you want on or off this list)