It could be out of necessity. Who knows what he is/was up to after he collapsed in 4.4.
Though given the voice and familiar look without the 'eyepatch', the person in the trailer could be likely him.
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Gunblade is not a ranged weapon at all...The gun there is for an extra "omph" added to attacks. In Final Fantasy (EDIT, cause I made a typo) VIII which I believe is the first (or at least, most prominent) appearance of gunblade, hitting a trigger button would shoot the gun mid-swing to shoot at an enemy and deal higher damage. I imagine that's the concept here.
Blade skills would be the weaponskills, while gun skills would be abilities that are used "mid-swing". There will be two or three weaponskill gun skills most likely (like the lvl15 ranged hate-pull skill every tank have), but I cannot imagine it having any more focus on ranged than that because...there's really no reason for that.
main npc wear special outfits, moenbryda dint wear a heavy armour either, with im concern about the leather jacket dosent mean thancred is wearing the actual AF of the gunblade job.
FF VIII, the main hero use a gunblade. Leon wasn't a tank neither was Lightning while at it, main reason why I'd choose the DpS path. Can't see how tanky it can be from a gameplay point of view. If its melee its just a one handed paladin.
Never seens the point of having a gun in a blade. Just take a shotgun and a shied for what it does. /shrug
VIII was the first, but even there the part of the gunblade wasn't used very much, so expect another melee tank.
In VIII, the 'shot' wasn't meant to hit the enemy, it was more meant to add vibrations to the blade and cause more damage that way.
You can see that in the opening cinematic of where squall and seifer fight against each other, and seifer pulling the trigger noticeably earlier before slashing squall's face.