With the Wii U release imminent, company president Satoru Iwata has teased announcements for Japan before the US event.
The man behind Nintendo Tweeted earlier today, confirming that "details of Wii U in Japan will be announced in advance" and that it "will be done in a way other than the conference" - most likely as a Nintendo Direct presentation, or perhaps a countdown website.
Nintendo of America will be holding their own event on September 13th, so plans for Japan are due before then.