According to Nintendo Everything, Nintendo will soon allow 3DS owners to take their physical game copies and convert them to digital copies that will be transferred to the 3DS SD card. The save date will also transfer over to the SD card which will allow players to take their games digitally on the go without the hassle of carrying game cards with you.
The 3DS supports SD cards in sizes to 32GB so there shouldn’t be a worry of filling up your SD card soon provided you swapped out for the 32GB size. This will surely be killer feature addition to the 3DS and its ever growing evolution into one of the best portables to date.
Source: Nintendo Everything