The way I understood it is there will be a story shortcut for at least HW to $NEWEXPANSION - probably a cut down, no fetch quests style thing. Still probably a ton of stuff - though I do hope they leave the option of doing it normaly as well.
And I'm guessing ARR story they might leave as is other than removing unnecessary fetch quests along the way as well. Or making them sidequests.
At least that's how I'd crunch it down currently.
The other approach is - here's a NPC talk to them - watch a 2 hour cutscene aka movie that will push you through the story.
There is a bit of a lore hook they can add that in as well... around the time you join a GC.