In an interview with Eurogamer, Tekken producer Harada had this to say.
Looking at the small screen and the big screen at the same time is pretty distracting for a fighting game. So we’re thinking of making it useful as a way of having shortcuts…Or, by making progressing through the game more convenient. Or by playing alone on the GamePad screen.
The latest game in the Tekken franchise — Tekken Tag Tournament 2 — is set for release on September, while the Wii U release still doesn’t have a firm release date.