The next Final Fantasy with a mechanical Omega weapon is 11. I could see them pulling fights from the base game, zilart, and promathia. After that its 13-2 and XIV.
Though I'd expect 9 since 6 is what Aikar said. 7 and 8 are kinda futuristic so the folk lore shit they pulled with the story won't fly as easily.
However a lot of mobile games are doing FFXI crossover shit and with the Nexon FFXI mobile due whenever it might be a good chance to get some XI hype going come Januraryish. XI already exists as an alternate universe or whatever.