Adding achievements and cross game voice chat for Wii U would be a nice start. The lack of games is also a problem, but time will fix that. The small user base is an issue too, but things will probably turn around when major 1st party games start to come out.
Add achievements to 3DS as well that are linked to the Wii U. Also, make it so you can redownload content in the event that the Wii U bricks or you buy a new system.
Basically it is minor logistical things that need to be solved. I would actually consider switching to Wii U over Xbox if they ironed this all out. Sony and Microsoft have these problems solved, but they just don't have Nintendo's unmatched 1st party titles. A cheaper price tag on the Wii U would make it easier to talk my friends into getting one too (they are buying one eventually, but it will just be for exclusives).
