Just personally I think the Wii U needs a super impressive 3D Mario game. 3D World was a bit of a letdown in my books. Not to say it wasn't a good game, but to me it basically felt like 3D Land but in HD. The game just feels like a series of obstacle courses given the lack of a overworld/hubworld (well a good one at least) and the timer and flagpole goals as opposed to the mission style goals of previous 3D Mario games.
To me Mario games work best when it feels like what you're watching is a window to another world. So what I look for is a cohesive world that makes sense. To me that's the foundation to which Mario was based on. In the original game Super Mario Bros, the first cutscene in the game is between 1-1 and 1-2. 1-1 is a standard on the ground level and 1-2 is an underground level, so between the two levels there is a cutscene showing Mario enter a pipe to go underground, which obviously make sense as opposed to him just magically starting the next level underground. So with that in mind I just found it disappointing that in Mario 3D World you have a silly 3D overworld which despite being 3D is essentially linear and you can go from a mountain to a desert to a snow level all in a couple of levels from each other. Despite world being in the title, it didn't feel like a world at all, just a series of obstacle courses. They were fun and wonderfully looking obstacle courses, but the game failed to capture my imagination at least.
So I'm hoping for a real home run of a 3D Mario coming up for the Wii U, something more in line with Sunshine and the Galaxy series that makes use of the Wii U's impressive tech to where the gameworlds can be vast and intricate and just fun to hang out in and interact with. There's a lot of unexplored territory with the Wii U tech that they can do with the Mario series, and as much as I'd like to see that next great Mario game sooner rather than latter, hopefully this news means that they're taking extra care in ensuring the next installment will be a top of the line game. Sorry for the long post but I'm a big time Mario guy (I just started replaying Galaxy again, great game) so I'm pretty opinionated when it comes to the pudgy plumber.