I think FFXIII will sell reasonably well, but not do much for the JRPG scene. Rather, it will reinforce "JRPG stereotypes" to people who are generally bored with the FF-jrpg genre or avoid JRPGs almost altogether, and the good JRPGs with quality gameplay innovation will still not be given the time of day by many a gamer turned off by the idea of playing another FF game, especially one that does not boast the budget and eye candy of FF.
To those who love FF, and just love FF because its FF.... other JRPGs probably wont seem nearly as good... I doubt we will see many coattails. With the exception of 12's gameplay (which I liked a lot, even if the story was meh and VO was PUKE - and which doesnt count since its gameplay has been tossed out the window for future design) FF series has not had anything major going for it since 7. Except GFX.... Square beats everyone in terms of GFX/Rendered cutscenes.... and GFX and rendered cutscenes make fans and sell games.
Though the list includes some SRPGs as well.. franchises and games such as Persona, Disgaea, Agarest, Ar Tonelico, Valk Chron & many more beat FF games since 7 in almost every respect, except GFX and cutscene budget. Especially in terms of real innovation, FF cannot hold a candle to the SMT Persona franchise. With the exception ofc of FF12's actual gameplay which was outstandingly good, and done by the same designer who did Vagrant Story which was also awesome... with a better story and characters it could have been an all time great easily.. but unfortunately most of the talented people in those departments have left SE over the years.







