I think the main thing that hurts the minor league sports, other than baseball, is that you really can't track their careers. With the MLB - MiLB model, all players have a chance to be called up at any time, or traded to another team that can call them up, they are 'Property' of that team. You also have the chance to have players come down and play with the farm clubs for rehab. I am not sure if Hockey is similar or has more of an NBA DL model, but Hockey is just hurt that it's a fringe sport, the AFL has a better TV contract than hockey. In fact, I think there might have been more Professional LaCrosse games on network tv lately. The only way for the NFL D-League to truely thrive would be for players to be 'property' of their parent clubs. Here is my short little model
Expand the draft to four rounds. Players are all givin signing bonuses and lower round players have a 3-5 year 'development' deal with the parent club paying around 50-75k a year depending on expereince, to be paid by the parent club. They are all property of the parent club and can be traded, moved up and down, etc.
This would hurt college basketball a little bit, but would greatly benefit the NBADL.