I would bet that Sharlayan and Hingashi will be the two halves of 6.0. We're heading into the finale of the Hydaelyn/Zodiark storyline, and both states are some of the oldest and most learned areas of the world, and are also both extreme isolationists. Also, apparently, there's an island nearby in the Northern Empty where the Roegadyn believe the world originated from, could be relevant. Basically, as far as we know places like Meracydia and the New World don't really have any connection to Hydaelyn/Zodiark, so that leaves us with locations that may at least know much more than they're letting on about the conflict.And my only problem for Sharlayan is that its such a small island which means that we are almost certain to be getting two places if Sharlayan is added in.
Unless they just go with space Allagans on the moon or something.