FFVIIs graphics would have to be completely redone for people to consider it a "cutting edge mmo" to leave WoW over. And if they redid the graphics that much, 99% of the people wouldnt even recognize it as being based on FFVII.

Storyline (both during and after the game) doesnt really lead to a MMO atmosphere, which usually includes some kind of world wide crisis in some way that calls for thousands of warriors to stand up and fight.

The only recent FF game whose world and storyline could actually lead to an MMO is FFXII, which already feels more like an MMO than anything else (not to mention it looks shockingly similar to FFXI already)