While in Japan for Tokyo Game Show 2012, we were treated to a brief demonstration of the upcoming Wii U version of Tekken Tag Tournament 2 (opens in new tab). The game was showcased by Tekken series director Katsuhiro Harada, and he talked up all the interesting new features in this version of Tekken Tag 2, which includes Nintendo costumes for the characters and a Mario-themed minigame. Afterwards we asked Harada if he had any comments on his team's involvement with another Nintendo game. In case you missed it, it was revealed a few months ago (opens in new tab) that Namco Bandai would be helping Nintendo with development of the next Super Smash Bros (opens in new tab).
When we asked Harada-san if he had any comments about the Tekken team's work on the game, he said this through his interpreter:
"It’s quite interesting to see the difference in the way that was presented to the press. In Japan, it was more accurate--there was a release that we (as in Bandai Namco) are working with Sakurai-san. But for some reason, all the publications abroad, the headlines all said “The Tekken team is working on Smash Bros.!” That’s not very accurate, because Sakurai-san is still indeed the person in charge of that project. We as a company--Bandai Namco, or Namco Bandai in the west--are cooperating with him on working on the game. That means using the experience gained in Tekken, and the technology as a base as well--in Tekken, but not just Tekken. So obviously, we’re cooperating with them, but it’s not “Smash Bros. made by the Tekken team!” Obviously it’s Sakurai-san’s project, so please don’t misinterpret that fact."
So while the Tekken team is assisting in the creation of next Smash Bros, they aren't the driving force behind it. That's still up to the franchise's director Masahiro Sakurai.