Well, take a look at 3dbrew.com.
It has a lot of information about it.
They even have a save decrypter called Save DeEncrypter3DS.
Also, this site has a list of known exploits (there are none
), known failures (there are many) and their current work.
BTW I have an idea. I know nothing about this hacking thing but...
I downloaded a program called Connectify, that turned my PC into a router, so I could access internet on my 3DS through my computer. The thing is: this program also allows LAN connections and Hotspot functions. Maybe... maybe it's possible to "disguise" the computer as a 3DS, connect it locally and use download-play, or other functionality . If it works, maybe the nintendo 3DS could download a modified demo from the PC.
I repeat, I know nothing about hacking, it's just an idea
Sorry my bad engrish ^^