All depends on the size of the development team they still have on FFXI. All of us of course salivate at the thought of another CoP type expansion (if you don't, get the *** out of my game) with beautiful storyline, difficult battles along the way, memorable NPCs, a restricted zone(s) only accessible through completion of the storyline, and solid rewards at the end of the path.
But if they simply don't have the manpower to produce anything except reskinning existing zones (see WotG, Abyssea) or adding pop points (VW) that add only new monster models (which I will be the first to agree are wickedly good), we can't expect a full blown expansion with new zones,etc.
The ideas and possibilities for an expansion have been talked about for a long time; we all know them. Its just a question whether SE feels they need to release a full "box sized" expansion in order to keep an already addicted playerbase paying them monthly or whether they need to put their resources, both money and talent, into saving FFXIV.