I just want Ian here to be practicing every day against Duncan. Dude will get much better much faster having to D up Duncan every day than he will over in Europe. Plus, you've got the added benefit of having Horry around to teach him some veteran tricks of the trade and learn the Spurs system.
Bring him in, let him practice every day with the Spurs, and send him up to Austin every night to play in the NBDL games. He'll come in much more ready to help this squad than he would staying in Europe for another year or two and then coming over and having to spend another year or two adjusting to everything - the speed of the NBA, physicality of the game, life in America, life in SA, his teammates, the Spurs system, etc.