Even if they couldn't do the whole world, just combing some of the zones would help a lot, to just reduce the frequency of zoning. Instead of having Old Gridania and New Gridania, having just Gridania, and the same with the other cities, would help. And if they can't combine all of Eorzea, what about combining all of Thanalan, or all of La Noscea? Both PS3 and PS4 support worlds or zones that size in other games.

(Then again, given how few housing zones their servers can support, maybe it's the servers which can't handle bigger zones. They seem to be running on some horribly outdated equipment. )