Let's travel back in time to a day before the Nintendo DS flew off store shelves. Behind the scenes Nintendo was experimenting with a touch screen adapter for the GBA. This technology was later used for a new handheld which gamers know very well now. However, a patent application filed by Nintendo in 2004 shows a different concept for the hardware.
An early Nintendo DS only had the top screen flip up and a different button layout. The X and Y buttons aren't in this prototype. A speaker takes up that spot. Game Boy Advance backwards compatibility wasn't part of the plan either. DS cards plugged into the bottom and there wasn't a second slot. Actually, this early design looks a lot like a rectangular Game Boy Advance with a second screen.