When it was announced that Smash Bros. would be co-developed with Namco Bandai, many assumed the game would include characters from the Tekken franchise. But Katsuhiro Harada has said that:
The fans, rather than asking about Tales or Gundam, or some of our other franchises, the fans abroad saw Tekken as one of the key words and took off on that.
…and:
We’re not really sure at this moment but when thinking of the player-base who is playing Smash Bros, maybe Tekken characters is something they wouldn’t want, so I’ve been pulling back on that a bit. But I don’t know.
It’s something I want. But maybe I’m not the average portion of the player-base.