I predict:
- The first instance will crash due to the influx of players. Y'all remember that first instance when 2.0 launched?
- People will probably be Level 60 with two days
- People will burn through the story just to be in time for Alexander when it opens up
- The final part of Heavensward will force players to skip cutscenes because the dungeon is too long (CM and Praetorium)
- New trials being like "Have cleared before. No new players. Watch a video before joining"

Just a couple of thoughts.