One of the biggest problems with the Wii U, was the inability to transfer your content and user data from one Wii U console to another Wii U console. This has been an issue since the Wii U was released, but it is a problem no more with the latest system update that was just released.
Once you have both Wii U consoles updated with the latest system update (which is version 5.1.0 for those scoring at home.) you are to use a process much like what the 3DS has. The data is copied from the source system to the destination system and then the source Wii U has its storage formatted to complete the procedure.
Using this transfer process, users are able to transfer their Nintendo Network ID, save game data, and download content to the new system. A step-by-step guide to the process is on the Nintendo support website.
Speaking of the latest update for the Wii U, besides the new improvements to enhance stability and usability, Nintendo has finally added the option to navigate the eShop using the Wii Remote, Wii U Pro Controller, or the Classic Controller. That is a fix that is better late than never and we suspect it will lead to more sales in the eShop for Nintendo.