I honestly believe Sharlyan might be the Hub City but the res of the expansion will still be Islabard, that does not mean it is inconsequential i imagine it will have a good amount of prominence like Ishgard in HW but since HW already saw similar concepts to some of these zones you are mentioning i do not think they will do that. Plus especially right now after ShB they really need to Fill in some of that World Map and some of these hidden zones you are speaking of do not really do that. Plus since we only get 6 zones in an expansion i want them to be cultured, The aetherial sea might be good for a dungeon but to make it one of the 6 zones of an entire expansion would just waste a zone in my opinion , you see it in the character creation screen there is not much there, in fact hardly any of these hidden zones you mention seem to have any cultures or peoples what so ever. After a shard hopping expansion we need to focus on further exploring the Source since it is the world we are most invested in and that includes finally exploring some long hinted at countries, not more isolated areas like these.