In my dream world, I had hoped that once Nintendo got the account system in order, they could potentially have the ability for you to choose what platform you want to play a game on.
For instance, you have something like Animal Crossing. It works amazing on the handhelds. Obviously we're getting a Wii U AC at some point, but until then, I'd like some alternate way to play. In this case, I play a lot at home as well, so it'd be amazing if I could say..put the system in sleep mode, and stream the game to the console. Then, pick up right where I left off. Playing on the big screen would be awesome, and if someone is also streaming the game to the console, you could have an optional camera/mic mode and have them appear up in the corner of your screen or something. It's annoying trying to talk to friends in the game, so I end up just texting mine when we're playing together.
Alternatively, some games on the Wii U would be relatively easy I'd imagine to allow for cross platform play. Particularly stuff like eshop games. Why can't I take Earthbound or Donkey Kong with me when I leave?
Obviously not every single game would be able to work, but I mean..shit i own Kirby's Adventure on like 5 different platforms. How hard could it really be? (I'm sure someone will answer this and say it's very hard.