After the first announcement in August, we now have a fuller idea of what's coming on Blu-Ray in September courtesy of a new official announcement. There will be three SKUs:
1. 9-disc, 6-movie collection (SRP $140, online as low as $90)
2. 3-disc, Original Trilogy set (SRP $70, online as low as $45)
3. 3-disc, Prequel Trilogy set (SRP $70, online as low as $45)
With 3 bonus discs in the full collection, we suggest waiting to see what the extra features are before skipping out on the full collection of films. Even if you think you hate the prequels, a key selling point for these discs will likely be deleted scenes which will not be edited back into the films, but were confirmed as supplemental materials. According to StarWars.com, the 3 discs will include 30 hours of bonus materials-- that's nothing to sneeze at. For more on deleted scenes, be sure to check out T-Bone's guide to this stuff for more.
It is unknown which cut(s) of the movies will be included, but it's a safe bet you will see additional changes to all six films. There's a CG Yoda which has been created and inserted back into The Phantom Menace, so that's one of many possible new changes to the films you have to watch for this September. (No exact date was given.)