The Wii U tablet honestly was made with the hope (on Nintendo's part) that it could spur the Japanese game community again.
Japanese gamers like to play their handheld at home since the TV is often times in use by other family members, Wii U was Nintendo's attempt to rectify that.
And yes they hedged very heavily on casuals who supported them with the Wii coming back for things like Nintendo Land, NSMBU, and Wii Fit U.
They were let down by both of those audiences.
Honestly it's a strategy that probably could have worked, but Nintendo got their knees cut off by the rise of Apple/Android, something they probably did not forsee to the same extent when planning for the Wii U began in 2009 or so. The iPad was not out yet, the iOS shop was just launching, and smartphones were still relatively in their infancy.
