This isn't a bad idea, and I wouldn't be surprised to see them do something similar in future expansions, but in this case opening the gates to ishgard is rightfully story driven. It's one that's been in the works since 1.0, that city looming over cch, for some nearly half a decade now, has been a long sought after destination. To allow people to hop right in after having waited years to see it would be a bit insulting. That said when we go to doma and ala migo for the first time a scenario like this is possible.