Title says it all... I have an Xduoo X3 running rockbox... fantastic DAP, dual micro SD slots, high end Cirrus Logic DAC. It just isn't quite as accurate as one of your DACs though... I'd love to see a dual slot DAP with a basic MIPS processor, just running rockbox with the great combo of 9018K2M and 9601.
Rockbox really turns the DAP into a flexible and reliable source.
You could release one with a Sabre DAC/AMP combo, wouldn't even need to use your own software, a Rockbox capable piece of superior hardware that would come close to the current Sabre DAPS that are around and over $1000, only the hardware alone could be around $250, it would be an instant winner.