Re-experiencing the story is likely the main reason for NG+. Not just for cutscenes, but also other things, such as talking to the random NPC's about the place at various times. As well as reading all of the text with new perspectives.

Changing major plot points is unlikely, because it would create far too much work to have so many events that can be altered and the many repercussions this has (As well as making it potentially mandatory to go through NG+)

Honestly, my major question about it is will it only be available for max level classes? Or would it become an alternate means to level up classes in lieu of dungeon spam/grinding out FATEs? Since MSQ is a pretty decent way of gaining experience. Even more so if you could return to specific points in the story to replay (So you didn't have to say, do all of 2.X MSQ before getting to level 50+ quests to level up with).