May I suggest that additional quest lines be added and only unlocked when you start your 2nd (3rd, 4th, etc.) job. This would give added backstory/lore/etc. and needed quest exp to level the added job(s) without getting into a boring grind. Admittedly it DOES mean additional work for writers and devs, but if Yoshi's goal of having FFXIV last for 10 years, they WILL be needed to keep people busy and exploring.
End-game content cannot do it all. There needs to be a way to keep those that want to keep adding jobs busy without getting them bored. Yoshi and the devs would be smart not to ignore the lower levels while adding end-game content.
FFXIV seems to be based on multiple swings through the lower levels and keeping them fresh with new and surprising new content and quests would do much in making FFXIV different from other MMOs that just concentrate on adding end-game content.