Personally I like your Titan Tank concept better than what they've ended up going for, but I can see why they didn't go with the whole thing in the end. It looks a bit too similar to the Ares tank and even has a twin-barrelled cannon as well (albeit in an over-and-under configuration).
Yeah, doing units at this scale means you have to push the silhouette a lot more. I do like the idea of a revolver-cannon style setup kind of like the Russian GSh-30-2, but it's probably too nuanced to use on something that's so tiny in the game.
I'm not exactly sold on exposed ammunition and recoil mechanism but then again, the turret would be much bigger, should you cram both inside. Of course, I'm not saying I don't like the thing - reminds me too much of the pure sexiness that is Russian Koalitsiya-SV dual howitzer.