Nintendo 3DS actually does not need to be hacked or medified in any way to play homebrew games or game backups. It is enaugh to buy flash card like R4, Ace Card or M3, which is preloaded with newest firmware. After that everyone is able to load it with any game backup (ROMs) or media, and play them on your Nintendo 3DS stright away. This does not affect 3DS or void it's warranty in any way.
There are M3 Zero adapters for Micro SD, SDHC and even the newest SDXC cards available, to use those in your Nintendo 3DS unit. It is known, that there will be 3D movies available for 3DS, but as you may expect, there will be more storage required for those. Also additional storage for your favourite mp3's, 3D photos and game backups will be necessity. Now there are available SDXC cards with capacity of up to 32 GB.