So I've had some time to think about it, and WFT's inclusion is no different from the Ice Climber's or Pit's in the previous game(s). They've all had one or two games before their SSB appearances.
The only problems that I still have with her are the fact that she's not a character from a game nor a mascot, which is what the SSB series is about.
But she might be fun to play as, and I don't have to use her if I don't like her.
So there. My two bits.
* Toad anxiously awaits Toad's announcement trailer.