@Unagi
That would be cool, but even in your example, the TV become irrelevant. All you need is the controller and the system hub, all I'm saying is why not take that one step further, and if they don't they are making the simpler
version and not just a simple game. I meant in no way meant to call the idea itself simple, as it would be awesome for a whole host of reasons, and even with your example, it still gives great credence to the 3DS being a controller, and if in the final version, the controller can't work outside the house, it would still be cool if the controller had StreetPass options.
@Those who think it would hurt the 3DSs market
Nintendo is not going to make a $200 controller. Maybe $100 (and the hub costs $200 for a grand total of $300) and it wouldn't have all the features of the 3DS, including 3D. The controller could have mobile versions of the system hub's chips (ala desktop vs. laptop GPUs) which would cost Nintendo less, because they would be ordering so many more of them and the mobile market is where every chipmaker and their cousins are pushing for right now. A single screen controller that can only take a few hours of full game, and play 'simpler' eShop games (maybe it will be in 3D?) does not compete with the 3DS, especially when that controller is made to more specifically be used with a home console, and the portable features are an added bonus, whereas the opposite is true of the 3DS, because it doesn't even have TV out.

@BnM
1st post: But why not just do that with the controller without any physical media? They could just include a 'digital copy' that can take out an upcoming portion of the game you're playing.
2nd post: Japan has plenty of WiFi, and Nintendo is a Japanese company, and Japan is also a place where the handheld is more popular than the console. America's big cities are catching up (if only ridiculously and horribly slowly) with Wifi, and every non-farming neighborhood in America has a Starbucks and/or MacDonalds within reasonable range. The 3DS is a good option to take a portion of Cafe games with you, but why not both? The controller has a screen, it would be a horrible oversight on Nintendo's part if the controller and the 3DS can't talk to each other.
Another thing I thought of, is the motion controller aspect. I'm thinking the handles detach from the screen, and become a nuchuck, Cafemote, duo, which could then also be used with the screen propped up with a kickstand on the battery pack. That's a lot of moving parts, so maybe not, but if they maintain their level of quality in parts, it could work.