Will we see a range dps that truly uses guns?

[Seraphor]

Machinist uses guns, it just doesn't ONLY use guns, and we'll never get a job that does.
Just like Bard doesn't ONLY shoot arrows, and Paladin doesn't ONLY attack with it's sword, they each have some kind of special or magical phase too.

They're not going to cannibalise existing jobs to make room for new ones.
AST isn't losing Gravity to make way for Time Mage.
NIN isn't losing Mug to make way for Thief.

FFXIV's job fantasy is based on more fleshed out jobs with multiple facets, because each one is a single job, you can't mix and match them to get the combination you want like in previous games, each job has to have enough depth on it's own. They specifically drew on inspiration/reference to FF1's system of jobs 'upgrading', it's built into the very building blocks of the class>job system, and that's where Thief > Ninja comes from.
And jobs can't be too similar either or share weapons, at least not within the same role group.

Now a 'Gun Mage', like FFU or X-2, could be a feasible option, as a magical ranged dps, as it would be our 'gun' caster. Question is whether we need a fourth iteration of a 'gun' job or if they have a better idea for our fourth caster dps.

[ThorneDynasty]

They're not going to cannibalise existing jobs to make room for new ones..

Yet they've constantly done that with the already existing ones. Hell, sometimes they don't even bother with the cannibalization, they just throw out the so very important identity skills. If WHM can exist without Protect I'm sure replacing Mug with a different flavor would barely even register.

[Thi]

Now a 'Gun Mage', like FFU or X-2, could be a feasible option, as a magical ranged dps, as it would be our 'gun' caster. Question is whether we need a fourth iteration of a 'gun' job or if they have a better idea for our fourth caster dps.

I'd switch jobs in a heartbeat for a Gun Mage.