During a shareholder meeting, Square Enix president Yoichi Wada noted that Square Enix is considering a Wii U version of its upcoming Wii RPG Dragon Quest X. According to a transcript of the proceeding, an investor asked Wada if he believed it was time to make the game for Wii U instead of the original Wii.
Instead of releasing it only on the successor system, however, Wada said that Square Enix was in the midst of "technical investigations" on how to support Wii U, and stated that the company "must consider" compatibility with both systems.
While the Wii might be on its way out, Enix's SOP with the series has always been to wait for an established, high-selling platform to emerge, and then put the game on that. A multiplatform release would be enough of a break from that tradition; we wouldn't expect Square Enix to stray so far as to launch the game only on a new platform.