I found this very interesting.
The basic premise is strong enough to allow great storytelling and, if Heavensward is any indication, it could very well be the best Final Fantasy to date in that regard.
Naoki Yoshida: To put it simply, the Eikons in Valisthea can kind of be compared to what you would call weapons of mass destruction or nuclear bombs.
Another key word in our story is the Mother Crystals and these realms' Mother Crystals are what you can call kind of like oil fields – in the term that they supply the land with the ether which is basically the energy which is used to to power magic.
The thing is, though, that ether that's contained in the Crystals has begun to dry up. And this has prompted some nations to basically try to invade other nations in an attempt to wrest away control of those remaining Mother Crystals. And up until now, the Eikons have never really been used, because again, they're like nuclear bombs so you don't use them. You just have them, and it creates this kind of standoff. But now, to wrest control of these Mother Crystals away from other nations, some nations have begun using and deploying these Eikons and basically bringing the realm into chaos, and that is one of our main focal points of our narrative.
The basic premise is strong enough to allow great storytelling and, if Heavensward is any indication, it could very well be the best Final Fantasy to date in that regard.