The US Constitution has this to say about elections:
“The times, places and manner of elections for senators and representatives shall be prescribed in each state by the Legislature thereof.”
Now let's say that you go to the Supreme Court and argue that "the Legislature" can also be a five member panel chosen by a nominating commission.
Do you think that would work? Well forty years ago, it might have worked, but this Supreme Court looks at actual words and no matter how you spin it, "the Legislature" only has one meaning. "The" Legislature is the Arizona House and Senate.
Here's a prediction. The US Supreme Court will determine that the "Independent Redistricting Commission" is not "the Legislature" and will void the current process of drawing congressional districts.
For a little background, check out Howie Fischer's article here.