Very poor compared to the Wii version's sales.
It would sell a few thousand at most for a few weeks but I cant see it pushing the Wii-U units in Japan. Now if it was released worldwide it could have some effect on the Wii-U but again wont be much as majority of the fanbase who wanted a online DQ would of already experienced it or have it with DQX Wii.
I would be surprised if it does do well lol.