This will never happen unless Nintendo exits the handheld business. As much as we (customers) want this, from a business perspective it does not make sense. You do not give out your secret sauce (Mario, Zelda, etc) to other platforms, especially ones that compete with your own hardware sales. Making this move would effectively kill the DS line. Why would anyone buy a DS when they already have a cell phone and can play all the games they want on it?
Well as I have never owned a DS I didn't know that it was playing legacy NES and SNES titles. I would have assumed that it was playing its own, newer games. I assumed they would release new titles on their own devices and release extremely old NES and SNES titles on third party devices in order to gain interest in the titles, so they can try to use that to bolster their own hardware sales