While the alternate histories and societies developed on each shard was one my favourite points of speculation, i think we should finish exploring the source first. The way i felt after this expansion was that it was all leading up to the Endgame of the Zodiark saga, which will probably be next expansion (Yoshi P. did say 6.0 would take us to the moon at one point) as such i imagine it will finally introduce us to Islabard and Garlemald (with the final mystery map being the moon) and wrap up this saga. Afterwards well there are still a couple of locations on the source we have heard about, Yoshi P. also said he wanted to take us to the New World (Hydalyn's version of the America's) and i could possibly see that being the location of the next expansions after the Zodiark story arch ends.