A few days ago, My Nintendo News posted about a Gamestop manager getting in contact, informing them that the release date of Super Smash Bros. for Wii U would be “around November 21”. They also stated that it would be bundled with one amiibo, the Skylanders-style figurines that were announced at E3. This seems like a very likely release date, given that Thanksgiving (and by result, Black Friday) is the very next week.
The date claim was further backed up by Reddit user “pwooj” yesterday, when he posted the above image to the /r/smashbros subreddit. If this date is starting to get around to retailers now, we may be able to expect the official announcement from Nintendo very soon. Just keep in mind that this date is the same release date for Pokemon Omega Ruby and Alpha Sapphire, so if it turns out that this rumor ends up to be true, you may very well have to make a choice between what game is more important to buy in the moment.