As a comparison to other hardcore/mainstream multiplatform games, how much have they sold so far on the WII U? Like Assassin's Creed 3 and Black Flag, Batman, Deus Ex, Darksiders 2?
They've all sold between 50,000 and 200,000 copies on the Wii U. That's just not much to justify making a port.
But I'd like to see Wii U owners make a petition of getting Dark Souls to the Wii U. The PC guys were very successful with their petition.