As people have stated before me, it makes absolutely zero sense for a dedicated Rockbox port for a device that runs an operating system we are capable of running on as a hosted application.
Raspberrypi, Beagleboard, Edison*, you Mom's fancy Android powered microwave, whatever...it doesn't matter.
If it runs Android or Linux, there is little to no point in porting Rockbox to the device as an operating system replacement when everything is in place to simply compile Rockbox for the architecture and run it as a hosted application. This would also force Rockbox into having to care about things it shouldn't have to care about: Bluetooth and WiFI are two examples of things Rockbox has no business handling.
[Saint]
*Also, just a quick thing to add about Edison, I have no doubt that it is theoretically capable of sound output, but you would be limited to Bluetooth or WiFi as all the views of the hardware I have seen suggest that there is no dedicated audio out.