Just a heads up, its very unlikely a flashcart will be able to load DSiWare and DSi only games due to the way they are handled. The games and DSiWare are encrypted and signed, meaning that the flashcart can not access the data, retrieve the headers or patch the games as they get loaded into memory to run the game.
So all in all, a flashcart on the DSi will let you play only DS games. So in the end, you'll just have a DS with no GBA slot x.x
At any rate, I hope to hear further news on all this. If somehow the flashcart makers can over come these problems (The encryption and firmware updates) then I'll buy a DSi. Until then, I'll wait until the battle between Nintendo and the pirates are over and see who will come out the victor before I waste any money on this.