fine if your a pro and can be sure that your mechanic will have topped up the battery, with a new bike in the team car should things go pear shaped.
imagine the idiot you'll look on the club run when you have to go the rest of the way in a stupidly hight/low gear (as the law of sod will dictate) when the battery dies. spare, oh i forgot to charge it…
when it comes down to a sensible price and uses easily sourced batteries (such as in your computer) or (more practically) works off a hub dynamo (but isn't that adding more weight?) let me know.
i won't be making the move to 11 any time soon either, marketing folks
edit:
why the need for cable? electrical wires perhaps, or wouldn't a wireless setup be better (just imagining the fun that the systems interfering with each other will cause in a bunch) for time trialling?