A few developers have spoken about how the Wii U pad can augment their game experiences, but it's not a perfect fit for all games. According to Katsuhiro Harada, head of the Tekken franchise, it could actually cause problems when it comes to fighting games. His team is currently thinking through how to make use of it for Tekken Tag Tournament 2.
"Looking at the small screen and the big screen at the same time is pretty distracting for a fighting game," Harada told Eurogamer. "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."
Some fighting games have used the 3DS screen for shortcuts, so his idea would be very similar to the use of dual screens for that system. The kind of precision play required for serious fighting games probably doesn't lend itself to the gamepad, so this solution probably won't be isolated to Tekken alone.