In fact, FFI have characters, cause' Amano depicted four people, WoL, Thief, White Mage, and a another dude with a sword, do you imagine traveling in a 3d rendered world with WoL and the others, with more plot.
Yeah they can keep expanding it, do you imagine seeing WoL, Firion, Cecil, Lightning or other people in KH, dude even the FFXI have some pretty cool characters, believe me. Not for being a online, it means it doesn't have a plot (it's like a Lord of the Ring, but with the FF Style.)