Title somewhat sais it all.
We know that they are wrapping up the ascians story line eventually. I think according to reddit 6.0 maybe 7.0. So with its wrapped up and us level 99/100 and them not pulling a wow and doing 110+, we will continue to get gear and ilvl (I am thinking FF 11).
But assume they don't stop with the expansions. I mean why would they? What new story lines would you like to see? Where could we go? To the moon and back? Or maybe more on "earth", distant lands never before seen, old familiar places from long ago. Maybe we could continue to explore ivalice, in less of a raid form. Technically they put in our world. We could explore other shards.
What would you like to do when the last ascian is dead and the credits roll? Where would you like to go?