Wii U will only support 1 tablet controller at launch but Nintendo is currently working on a patch to make multiple tablets possible but it won't be ready until way after launch.
http://www.egmnow.com/articles/news/...-after-launch/
Nintendo is also working on a patch or ways to minimize calibration issues that could pop up from certain Wii U games at launch but only a few games (no ports) seem to be likely to be affected.
http://kotaku.com/5918070/nintendo-h...ration-problem
Iwata also recently confirmed the Wii U will allow developers pretty much a free reign on what they want to do with DLC while also promising to allow free-to-play games to be possible on the system similar to the PC and PS3 to help bring more games to the console.
http://www.screwattack.com/news/wii-...sactions-space