Mills looks good, but he still has the same limitations and those aren't going to change. He's a shooting guard in a point guards body. He can probably run the point better than Neal did, but he is always going to look to score first, pass second.
That being said, right now it's not as much as Mills playing himself into the job, as it is Nando and CoJo playing themselves out of it. They have both looked pretty mediocre during the preseason, whereas Patty has had some good games and been a steady force with the bench.
Mills seems like the obvious choice to start the season, but...Pop's mind works in weird ways.