Sorry I'm super late to reply to this. Work and stuffs~
Anyways, unfortunately I've never actually gotten the chance to complete FFXII so I didn't know that the Viera eventually master the effects of the MIST, but now I'm super excited to find out since I did buy the PS4 version awhile back!
It wouldn't surprise me though if Yoshida allowed us to explore pieces of the alliance countries under Garlean rule/occupation that Othard had contacted! Dalamsca is definitely on my number one list along with any other parts of Ivalice we get to explore!
If we really do go to the Eryut Village to ally ourselves with the Viera there in order to help push back the Garleans in Ivalice (and particularly Dalmasca) I probably gonna die and go to heaven seeing Eryut Village recreated in FFXIV!
I can also see a reasoning for us to go to the Viera's home in 5.0, too since the Garlean Empire still occupies Ivalice they probably would have tried sealing of the Viera's Forest completely from the outside world and make frequent attempts to penetrate it in order to gain whatever secrets lie hidden within it.
The Feol could easily be byproducts of what Viera that were captured/ by making an attempt to leave their forest home at one point or another for whatever reasons they had and cross breeding with the Garleans as a result, producing the diluted clan Feol that the Pure Blood Viera despise so much because of their Garlean heritage! Sorry if all my ramblings and such don't make any sense. It's late here and my brain is trying to fall asleep. XD