Awesome artwork! I can tell you before anyone else chimes in that from the graphical side of things it would be very possible as all ranged weapons have multiple bones to use for animation (although this would just use one). Missile and explosions could easily be made as well.
I think the main thing that would hold this back from becoming reality (aside from them possibly not wanting to put the work into making 7 new animations/sets of weapon skills) is getting them to accept something of this.. I guess mentality? I dunno the word im looking for.
Like the area with the monorail, it was deemed not fitting due to its advanced technology. The 'cannons' we have currently look like oversized guns, and I think they more or less try to stick to the more olde timey sword and shield, leather and iron vs dragon and orcs mentality (despite having complete departures from this theme via things like Armageddon).
I for one would love to see something like this in the game though. At one point I had made a gatling gun for my Galka so I can vouch for this being possible to make. The general idea of the need of a AoE weapon with high delay, essentially a form of magic for melee users, I think is a great idea and would be great to see!
Still waitin for dat Engineer class! ;;
-Edit-
Oh I found a picture of the gatling gun back when I was working on it!
I miss big bertha :\