I don't think that maybe even a bigger part of the Wii U audience isn't interested in something like Dark Souls but I think that most of the Wii U owners who are interested in games like that have also a PS360, PS4/XB1 or PC so that it won't really change much about the overall sales of the game.
Most people who own only a Nintendo console are probably more fans of other games so that it doesn't really make sense for the developer to develop it also for Wii U if most Wii U owners interested in it will buy it for another console otherwise.
I can only speak about the people I know in real life and most who own only a Wii or Wii U would never touch this game and those who have a Wii or Wii U and also an as example 360 (that's the combo most of my friends have) will buy the game with or without a Wii U version.