I don't think they're going to do that at all. WoW went the extremely lazy way with that. FFXI, which is actually older than that, changes cutscenes and the characters involved depending on the content cleared, which is actually really impressive since the events in question change the power structure of an entire city. XIV actually does this, too, to a certain extent, for example, you can guarantee Alisaie will have different dialogue when she appears if you've cleared Coil. The level 60 SMN quest dialogue changes based on if you've killed Lahabrea first or not. Estinien has different dialogue based on if you've done the DRG questline. So on.
FFXIV adores its continuity, as they should. They aren't going to toss it out of the window.