In a more happy line of thinking. Add Critical Engagements to the overworld. Those seem to be what people enjoy in Bozja so rather than have a whole zone dedicated to them, just add them to the already existing world. Much like how Ixion needs (or needed?) an item for people to be able to damage him, make an item that gives you a buff and you NEED that buff to damage anything inside this Overworld Critical Engagement. This item is gotten by spending bicolor gems and maybe each map has its own item you have to use.

People get their open world content they want, Square doesn't have to make a entire new area for it, and it uses the one thing I repeatedly hear is good about bozja

Edit: To keep it going throughout the expansion, add the Eureka/PotD/Bozja style lockboxes