US will not allow that to happen. After Iran turn islamic in 1979 and took away their most advance fighter(F-14) that time, USA realised it cannot allow to sell its more advance weapon to even great allies. Which is why US do not approved F-22 to Japan.
Same as US will not allow a nuclear armed Japan. If Japan insist on acquring nuclear. The 28000 US soldiers in Okinawa will strike Japan first. Today, Japan may be US friend. But US never totally trust non white Allies. Next day, Japan maybe US enemy.
US is encouraging Japan to bark at China but it will not allow a nuclear Japan. All Japan nuclear facilities especially the highly enrich uranium is still under US monitoring.