To be really, brutally honest, I don't see Old Sharalyan appearing at all - it's on a tiny island completely isolated in the top corner of the world map, and has a policy of very restricted dealings with the outside world. That and it's kind of a FF tradition sadly to talk up certain places, and yet never have the player ever visit them at all (FFXI was full of these - Tavnazia (other than the ruined cathedral and aqueducts), the mithra homeland Ozhirlya, the whole eastern portion of the Iradjia continent where the far eastern nation Tenzen, Iroha, and the NIN and SAM Jobs came from was, the far northern continent the orcs and gigas came from, etc etc). Sadly I see the same happening here - places like Old Sharalyan will be mentioned constantly, but never actually visited. I think that's just being realistic.
As for the final zone, I think it's clearly going to be the Moon, and in keeping with the FFIV references, there will probably be a surface area like the Lunar Subterrene in FFIV, and an underground area that is decidely more bonkers and surreal the closer the player gets to Zodiark's prison (picture the Lunarian city in FFIV or, as Shougun mentioned, something like
Terra from FFIX).
Either way, we'll find out soon enough!
