We have been thinking about different quests and area accesses but definately you are not required to make all the missions to enter some specific areas. We will make some final decisions before the launch, and the areas will be announced in the news. Such as:
Muggy Plains, Corruption Hole, Razachai, Inquisition last mission area, Warzones etc. Maybe all get access through shortcut to Banuta 1st floor but lower ones needs quests? Also things like Djinns, Rashid and Postman Quest missions should be available for all, don't they?