I'm not saying the new gun class is going to be... but its going to be...

[Freyt]

I have heard nothing about anything saying that the class is alrdy established in the plot. Where did you hear this? You got a link or anything? Are you sure you arnt taking words differently where they mean about how Musketeer is already established?

The main enemy of the plot, and someone in the same army with a peculiar connection to Cid also part of the main plot and still ongoing:

Given two characters have the same style of weapon means it's an actual taught style of fighting, and not just something random. There must be a history behind it, and we already know there's at least some kind of future to it, with the current plot of the Crystal Tower events.
The other gun weapons used by the other generals probably won't come into play as they're all dead. Nero had a hammer but he has only used that in one fight, and has before and since then been using a gunblade.