I've always felt the main story was too forced since ARR hit, but blocking the entire expansion is taking it a bit too far. The most basic solution would be:
Have a stand alone quest for entering the new expansion zone, it would require you to have a level 50 job.
Once inside, players can pick up the next main story quest where it left off, "Before the Dawn"
This way players would be able to explore the new area at least, and do solo activities like leves, gathering, crafting, flying etc.
