I would agree that porting rockbox to the physical platform would be a waste of time. Not only will users not be willing to reboot it into rockbox, but they already have a plethora of dedicated full screen media players which use either the touch screen or buttons. Running the emulator would be a good idea, but it would probably require reworking the GUI to look normal without holding the device sideway.
Another major issue the is the horrible sound quality coming from the device, I tried to use it as an MP3 player, and the sound it produces was equivalent to a $2 pair of headphones.