As much as the Wii is popular in Japan, the DS is moreso. Logic dictates that the DS DQ should sell more. Especially since all the DS DQ games have been selling well over there.
However, there's a chance that, since DQX is coming near the end of the Wiis lifetime and it is coming after DQIX, it could have massive hype and feel like an 'upgrade' to the last game. But Japan doesn't buy games always based on graphical upgrades. In the end, I think both the Wii and DS DQ games will sell near each other in total sales, but the DS one will come out higher.











