I actually think it would hurt parity. Because instead of Duke, UNC, Kansas,
and Kentucky having to re-build their entire teams every year, they will have more 3-year guys. Look at where the blue bloods have been the past few years... the one-and-done route is not a great predictor of team success. It's been five years since Kentucky was in the Final Four.
For example, let's say the Top 15 players in a class go to this development league. That means the 16th ranked prospect becomes that top player available for colleges. This guy was previously going to schools like Virginia Tech or Wichita State and serving as the core of the team for three years. He now goes to North Carolina and plays for three years before declaring for the draft.