I have to agree with Roto, sorry to a spoilsport. The two wouldn't really fuse well, given that Final Fantasy characters are much more fleshed out in terms of personality and character interaction, and as a result, it would be hard to make a story for the game. Also, it would be really hard to come up with a middle ground between Soul Calibur's and Dissidia's fighting styles, seeing how they're vastly different (fusing Soul Calibur's mainly melee fighting style with Dissidia's physics defying fighting style would be really difficult).