So far, Jim Jackson has shown better playmaking skills than either JJ or Barbosa - though his normal mindset may be more oriented toward scoring than playmaking. It could be that currently he's trying to win over the coach and other players with good team play. At this point I like JJax for this team but I'm leery of someone who has been traded so often.
It might be a good move for D'Antoni to make him the backup PG as well as spelling JJ and Q - that makes him a more important member of the team. The other thing it does is make it harder for him to feel like he's shown that he ought to be a starter, say, in Q's place. D'A could transition to that by bringing JJax in when Nash goes out but have JJ be the nominal PG for a while. Of course, it might be a bad move... maybe it's better to keep him from feeling too important to the team, lest his ego get over stimulated.
I'd like to see Barbosa get a consistent spot in the rotation - and not as the backup point guard. Have him focus on defense and racing up and down the floor. Though, still with the green light to score within his normal game. Start him with 5 minutes per game and let him try to earn more minutes with his defense and hustle. The goal can be stated in pretty concrete terms - you want him to able to take Bibby, Parker, Mobley and Ginobilli out or their games while adding to the pace.