Slight correction from earlier: It was Mario 3D World and ALBW that released on the same day last year - November 22nd. The Xbox One also launched on this date. In the U.S., it is unquestionably better to get your big titles out BEFORE black friday, even if there is competition (including your own), than to release AFTER black friday just to space things out. That's THE day, the biggest U.S. shopping day of the entire year. If Smash is not out in America before that day, then something has gone seriously, seriously wrong.
I would put money on the 21st, and this only cements it. The reason the announcement hasn't been made is because they need to hold off until after the 3DS version is out worldwide. Nintendo will put out a press release on October 5th, and that's when we'll get our date - either in that PR or in a direct shortly after.