Alright, so if I repeat something or missed the point... ignore this, otherwise read on. I might have become a bit excited and jumped the gun...
I had an idea for an RPG once that I codenamed "A Tale of Three". The reason was because it wasn't so much an RPG as it was three 10 hour storylines interwoven and connected. In terms of D&D there was a Lawful Good character, True Neutral character and a Chaotic Evil character. With any of the characters during the game you make choices pertaining to their individual stories, however, at anytime you could quit and save your progress and start up into another save. So you were saving not only your game progress but how the world itself has progressed because of your actions.
For example: You start up the Chaotic Evil character, enter the first village and succeed at burning it almost wholly to the ground. You leave the rubble to outside of town and save. You exit out and realize you've completed 1% of the Chaotic story. Now you choose the Lawful Good character and start up. You decide to enter this smoldering rubble of a town and suddenly your faced with a whole new list of options. Also, as you progress through the game your choices also can give your Good character access to more evil options perhaps turning him into a feared bad guy, or the Evil character into a hero.
It's almost a choose your own adventure novel in game form. I know the programmers would loathe me, but a 30 hour replayable RPG sounds good in my mind, you could even lower it to 3 six hour stories and hope the replayability keeps them entertained for longer.
Just an idea I keep rehashing and loving... it's my dream game!