Sharlayan is just an island far away from everything else and is roughly the same size or smaller than Vylbrand (where Limsa Lominsa is). They are nowhere near Garlemald, there's an entire Eorzea-sized ocean in between the island and Ilsabard. On top of that, they're extremely isolationist and want nothing at all to do with the rest of the world's politics. That's why Lousioux and the Circle of Knowing left to Eorzea. Considering they've been neutral for a millennium and a half, I don't see that suddenly changing or giving us any reason to go there and do adventures in the Sharlayan countryside unless something drastic happens in the next two patches.
Hopefully before the next expansion happens, we off Zenos and leave Ilsabard to the remaining legatii who are becoming warlords and we go and do something new and interesting that doesn't have anything to do with Ascians, Allagans, or Garleans. I want Shadowbringers to be our Chains of Promathia, where the story is (mostly) ended, the world is saved, and the next expansion is free to be it's own thing. Doubtful, but I can dream.