Do not hold your breath for any old world content. You will die, and everyone will be sad.
The narrative play section starts with examples of trying to build game scenarios out of story engagements. From what I've heard it doesn't do anything more or different or more interesting than any couple of players would have managed just making it up themselves. The remains of the section is a bit more interesting, as it covers specific campaign formats - including a version of path for glory section that covers more than just chaos warbands, though less than everybody (order and destruction only get rules for specific subfactions). Also map campaigns, tree campaigns, etc. Not bad stuff, but no great detail, either, still mostly just leaves things up to you. For map campaigns, from what I hear you'd have more to go on adapting the old fantasy map campaign rules than working out of the generals handbook.
The difference between narrative and open play is... basically nothing? Open play is just where they put the multiplayer rules is all.
It's worth noting that the faction traits, commander traits, and artifacts are presented separately from the matched play rules as something to use in AoS games regardless of how you're playing them. Honestly, those will probably prove to be the most interesting & relevant additions offered by the GH for narrative players.
