A reservation card posted by Twitter user BluesDriveBuster suggests that Super Smash Bros. for Wii U will come November 21st.
The reservation card comes from a chain of superstores called Fred Meyer (guess what the founders name was?). No official release date has been announced for the game at this time, and the card itself says the release date is subject to change. It's possible these are place holder reservation cards printed early so the store may be able to sell them without knowing the official release date. BluesDriveBuster later tweeted that they had the cards on display and Nintendo later told them they could not display the cards yet.
Whether any of this is true remains to be seen. The 3ds version of the game releases October 3rd, and the official launch window of the Wii U version is set for 'Holiday 2014'.