Well, this is my thoughts about the chance of FFXIII reaching this level of sales.
This game is sure to make near 1.5 million in Japan first week. What leaves 3.5 million to western players to fullfil, other games like Halo 3 and GTa IV did superb in west, but couldn't count with Japan. FFXIII can do superb in Japan, and Great in west.
Sure, it all depends on how the marketing for this game will work, but if it have the same levels of marketing as Halo3/Gta IV/FF VII it's pretty possible
This game have a high expectations not just for reaching sales marks, but to regenerate the interest in the series in west and regenerate the JRPG genre. Look what FF VII did for FF series, if it wasn't by that game series wouldn't be the hit it is nowadays, and JRPG would be more niche that it is today.
The whole japanese developers of rpg count on this game to bring the JRPG genre once again to the graces of mainstream players, and reafirm japan as software producer.
