How could that possibly work? There are some DS games that only use one screen and don't use the touch capabilities so these games wouldn't be a problem to run tv-out, but how could you do the ones that require two screens? Would the tv do one screen and the DS do the other? Or would the TV do both one on top of the other? And then what about the touch screen games? How could a game that makes heavy use of the touchscreen work on a tv? You would need to look at the DS screen in order to play them, so it would defeat the purpose, unless you wanted to have a room full of people watch you play.
The GBA's screen dimensions are not the same as a TV's, yet the Game Boy Player worked like a dream. It blacked out or used a border to fill in the extra space. There is no reason this couldn't just show the two screens on top of each other like if I make it so I can see two programs at one in Windows. And then you have the option to focus on only one screen if you desire, which would be more zoomed in. The touchscreen works the same as it does. If I have to look down, I look down. That's just the reality of using a touchscreen.
Though since the touchscreen is just a glorified mouse any way, using the Wii remote as a pointer could work as well, if they wanted to go to that trouble. I wouldn't expect them to.
If we can look at DS screenshots on our computers then we can see two "screens" of DS play going on at once on a TV.
I'm suggesting this as a feature of the system itself so it isn't like the Game Boy Player where someone could get that for less money than a GBA. If I have to buy the system and I have to buy the games, then Nintendo still gets the money. Nintendo expressed concern for vision problems with the DSi XL and this is somewhat related to that. Someone who finds the screen too small or that using a portable is too hard on their neck can still be a customer. They can only make the screen so big while maintaining portability.
I only buy portables to get the exclusive games on it. The portability is of no use to me. Nintendo released both the Super Game Boy and the Game Boy Player so at some point they felt there was a market in catering to people who wanted to play their portable games at home on their TV. And the PSP does it so Sony thinks there's a market for it. It's been done and is done now so please do it with the DS2.