Jacien, firstly and most importantly, your observation that a crossover has been done in another game before is not in any way an argument against my claim that it should not be done in this game.

Secondly, your example is disingenuous. The plot of Final Fantasy Tactics had nothing to do with Cloud whatsoever. The plot of the game, and the heroes and villains of the story, pretend like he's not there at all. If Lightning were to appear in Eorzea for no reason at all as a promotional event, it would be a bit insulting, but it would be analogous to Cloud in Final Fantasy Tactics. However, Yoshi has promised us that "I'm going to make sure that it's natural she's in this world. Is she going to stay here? What's going to happen to her..? All that is also going to be mentioned in the storyline - it's going to become a natural part of the history of Eorzea." Yoshi has said Lightning WILL be part of the lore and story of Eorzea. So it's apples and oranges. My claim above is that making crossover characters intricate parts of the plot of this game is a huge mistake.