I don't have a problem with defensive rebounds being part of def rating since defense is about limiting possessions (especially quality possessions) and a rebound is a certain way to end a possession, but other things need to be looked at as well. Which has me thinking:
I would find it interesting to add in rating numbers for clutch, leadership, quickness, speed, and hustle. Imagine those numbers for people like Rodman, Bird, Jordan, Olajuwon, Russell, Rondo, West, and others. It would be difficult to do, but it would be worth the effort. Think of the value added to a guy like Iverson that seldom gets used in the sim because the sim does a poor job of capturing how devestating his crossover was and how he could blow by someone. The same with DWade, Clyde Frazier, Tim Hardaway, and Isiah.
Think about how those would effect defense. Rodman's hustle. Bird's clutch, quickness, and hustle. Rondo's speed. Magic's clutch, leadership, and quickness (which is so underrated...Magic wasn't the fastest guy, but he would be on people and then by them before they knew what happened). Jordan's everything. One of the most frustrating things in the sim is that it fails to capture the true characterstics of the gods of basketball. How many of us have seen a last second shot taken by Wilt or Russell when MJ, Bird, West, and/or Magic is on the team? Think about how cool it would be if you could say "Down by 1-8 points or up 0-4 points with 1 minute left I want the offense to maximize opportunities for X Player." On defense you could say "Down 1-8 points or up 0-4 points with 1 minute left I want to assign X player as a stopper to guard key clutch player".
Just some random thoughts.