An open topped version would essentially mean a complete redesign of the turret. Apart from interior detailing we would also need to detail the loading mechanism itself.
It is no secret that modern self propelled howitzers like the Paladin is a major source of inspiration for the design, so I'd sort of prefer to keep it a closed top turret to keep it in line with the original design philosophy (also helps differentiate it from the open toped DRM artillery). Although we did discuss an open topped artillery version at one point, there is another more practical reason why the closed top has some advantages for this particular design:
The tricky bit here is that we are essentially dealing with a fairly tall APC hull where the gun needs to be mounted on top. Most open topped artillery pieces I've seen are flat trackbeds that only need to accomodate a driver. A flat hull makes access to loading mechanisms easy. We're trying to avoid something  that looks like an APC with a gun glued on top and the turret helps to camouflage this (we could assume that recoil and loading mechanisms can extend into the hull). As a comparison try adding an E40k Basilisk gun on top of a Chimera chassis: It looks weird! The Basilisk hull is somewhat lower than the chimera hull to compensate for this.
On the Cyclops mortar we're trying the open topped thingy but ask Otterman how many headaches this has been causing ÂÂ
I'll probably need to explain some of the woes once we have a 3d pic ready for you
As mentioned earlier, the Modular tank system has some advantages but it also has a few drawbacks since every weapon system need to be made in such a way that it can be mounted on a standard chassis without looking completely out of place. Even though the majority of GWs IG tanks are based on the Chimera chassis it is actually only the Deathstrike and the Manticore that share the exact same hull. The rest have purpose built variant hulls. We're tryig to use the exact same hull for the entire range, so every now and then we do run into trouble
Major redesigns like those suggested are unfortunately not possible at this stage, but we could have a look at details like the muzzlebreak. Basically we were just trying out something different not commonly seen on Sci Fi models, but it could be changed to look more like a Paladin muzzle if there's a great demand for it. ÂÂ
 
