It's not the future of FFXI or any other FF game. It's its own world that just so happens to reference other FF games, but giving them their own spin to make them fit with its own lore. Nowhere in the lore book does it mention anything about Vana'diel, nor anything about Altana, Promathia and the Zilarts. Heck, Bahamut isn't even an Astral (and doesn't exist as a Primal until the war against the Allags and before then, he was just one of Midgardsormr's children), which is enough for me to say FFXI is not FFXIV's past.