The BrickBone project is still in the works. It too will be entirely open-source.

The BrickBone will interface LEGO Mindstorms motors and sensors with the Raspberry Pi.

Will it be compatible with the beaglebone white?
Will it be compatible with ev3 sensors?

I can see the 2 arduino on the brickbone. Did you consider using the 2 pruss CPU embedded in the beaglebone instead of the arduinos? I guess it would be more work on your side, but it might less expensive for the hardware.