The official Japanese Twitter account for Super Smash Bros. updated its status today, revealing that a new livestream on Nico Nico Douga will premier on September 12th at 7pm. The times convert to other timezones as the following:
America (East Coast): 06:00
America (West Coast): 03:00
It will naturally be showing off some new gameplay for the 3DS version of Super Smash Bros., set to release on September 13th in Japan and on October 3rd in North America, but no other information on the contents has been revealed at this point. You can catch the livestream here.