There is no way you can emulate GBA advance games on the Nintendo DS. Think about it, we have RAM expansion packs, some giving the user up to 32 to 64 megabytes of extra RAM while the DSi will only have 10 megs of RAM. Now if we don't have a GBA emulator with 32 Megs of RAM, how do you suppose we'll have one with just 10? The problem here isn't the RAM but its the processing power of the DSi. Currently theres no way to run a GBA advance game from the Nintendo DS. To naively run GBA games on the DS, you have to place them in the bottom slot (Slot 2) and boot up the Nintendo DS in GBA mode which can't be done with slot 1 cards.
So unless Nintendo has changed the hardware and firmware in a way to be able to start up GBA games from the Nintendo DS, it would be impossible to play them on the DS. You could technically emulator GBA games, but they would never run at full speed. You'll most likely get them playing at 1-5 FPS at best.
Now for all of you saying "The DS still has the hardware", yes, it still has the hardware because normal Nintendo DS games require them, though it doesn't mean that the processor still have the routines to play GBA games. Currently they work two ways, when you boot a Nintendo DS game, one handles displaying the images on the screen while the other handles the sound and processing power while if you boot the hardware into GBA mode, they mimic the hardware in the original Gameboy Advance console. So technically, the Nintendo DS have two modes of use with the GBA functionality having a chance of being removed as well as the GBA slot.