After playing around with the recent discoveries made by James Whelton, another iPhone developer and hacker Steven Troughton-Smith has found DFU mode in the 6th-gen iPod nano which is similar to the one found in all iPhones and iPod touches.
To enter DFU mode on iPod nano 6G: hold down the restart buttons until you get a black screen (it reboots twice) and iTunes sees the device and alerts you.
Afterwards, modified iRecovery to work with the iPod nano (had to add its DFU/Recovery USB ID) and allow it send files, and tested with some files I had extracted from the iPod nano 6G firmware (using the extract2g tool somewhere from http://www.freemyipod.org/ ).This will hopefully open loads of new possibilities in not-so distant future, like installing custom firmware files, apps and more.
disk.fw and osos.fw work (one boots disk mode, the other boots to a homescreen). The other files make the nano boot to a white screen, but go no further.
So, basically, it seems we can send encrypted firmware files to the iPod, and have them execute, similar to what is used to jailbreak the iPhone. If the nano rejects the file (i.e. unsigned, invalid), it reboots.
While this by itself isn’t that cool, hopefully the info will inspire someone else to finally hack this thing and give us custom ‘apps’.
However it is important to note here that the jailbreak hasn’t been achieved yet, because there is no root access on the device. But it is a step in the right direction. And as 9to5Mac points out, someone from the iPhone Dev-Team will have to find an exploit in the OS before the jailbreak can be achieved, allowing custom firmware files to be installed on the 6th-gen nano.