This is more of a Hardware suggestion instead of a Feature suggestion: Grounding Plugs.
I use the handy cables that came with my TT's, they have Red/White RCA's molded together with a grounding cable. There is a couple of inches of leeway at the end of the cables, but its still kind of a pain to ground them to the mixer while plugging the audio into the breakout box.
If the box had a plug for the grounding wires, it would be quite swell. I figure this wouldn't ground properly unless the power supply was attached (ie. no USB powered grounding).
Doesn't seem like a HUGE added expense when the next revision is released.