it depends, the story of FF13 was not very good imo, i'm not sure if its the same script writer, or if Nomura is personally penning the script. no idea, its possible that because of the world map, airships, etc, it will be better gameplay wise.
but i highly doubt the sales can be better than FF13, i myself wont be picking it up on day one, unless its reviewed really well. and i think there will be many fans who do the same. the only thing is i dont think Versus will be out next year, from what SE has said recently, i think early 2012 is more likely.
Nojima's Writing it. He wrote 7,8,10, Crisis Core, and Kingdom Hearts 2. and co-wrote Kingdom Hearts (With one of the co-writers of FFXII Daisuke Watanabe, and Jun Akiyama) and X-2 (withDaisuke Watanabe again)