A few thought on this... It's 2015 and Wii was discontinued in 2013. How relevant is it still to update support for backwards compatibility on Wii U? Just like subsequent PS3 models since launch had less and less backwards compatibility options as it was no longer relevant, ultimately leading to a PS3 without backwards compatibility. This is much akin to the Wii Family Edition and Wii mini, both which removed GameCube support. I'm guessing that Wii eShop titles just lay the groundwork for a Wii U without backwards compatibility. Even though for the Wii U it's mostly software (as opposed to hardware components in the PS3), it's still an aspect Nintendo would need to keep maintaining and updating, and it's currently the only way for any kind of homebrew to exist on the Wii U. That's two reasons Nintendo would want to get rid of backwards compatibility on Wii U: to reduce costs (R&D and maintenance) and to lessen the likelihood of homebrew on Wii U.
So don't get any happy thoughts. Just like Wii mini was released without online support, much to the hate of critics, ultimately leading to the fact Nintendo Wi-Fi Connection was discontinued in its entirety, I believe Wii eShop titles on Wii U are just the first step going towards a Wii U without backwards compatibility.