What exactly will be shown during the upcoming show is currently unknown.
Nintendo has announced that a new Nintendo Direct will take place on Thursday, September 12th at 4:00 PM Moscow time. The broadcast will take place one day before the 40th anniversary of Super Mario Bros.
What exactly "Big N" will show is still unknown, but it is assumed that the company will announce the release date of Metroid Prime 4. It is also possible that Nintendo will present a new project in the Super Mario series.