That's why they used the American M10 Wolverine TD and stuck a 17 Lb on it and called it the Achilles... Loverly.  

From a functional rather than aesthetic perspective, rear-facing cannons work just as well as forward-facing ones.  But there are a few drawbacks to this design:

1.  No direct-fire support for infantry.  We used to train using the M109A6 Paladins from our field artillery component to create breaches in MOUT situations.  The best way to enter a building at the ground level is to have a Paladin blow a hole in one wall, since you know for sure that room is clear.  This configuration would be severely limited in that environment, no matter how good the gunbunny behind the wheel is.

2.  Resupply needs limit the shoot-and-scoot capability.  A self-propelled gun carries limited ammo onboard, and depends on a mule to resupply it, usually another tracked vehicle that can back up and use a conveyor belt assembly or derick to push rounds over to the gun.  If a mule were to do so for this thing, it would have to be from the side.

3.  Firing and loading.  The Minotaur's twin guns would have to fire simultaneously, or else in a sequential fashion with reasonable time in between.  Reason being, firing one gun would cause the vehicle to jump enough to throw off the register of the second gun, so its round wouldn't land where it was needed unless they took the time to reposition the vehicle and ensure that they are properly registered.  Plus, looking at the pics on FW, one crew loading a gun would have limited space in which to cycle the other breach, while both crews working simultaneously would be getting in each other's way.  There would be the very real possibility of someone losing a leg to the recoiling breach of one gun tube firing while trying to load the other, so sequential fire would be difficult.  So either way of operating, using two crews, is problematic.  A third possibility would be to have a single crew working both guns -- load both and then fire both simultaneously.  This would be exhausting for the cannon-cockers and would return a lower rate of fire than a crew working a single gun, since there would longer lag time between firings.  

Better solution:  Autoloading single gun tube.  But that's just my opinion.

It reminds me of the concept pictures floating around of the FW daemon engines, rather than some imperial design.

Sigh. Another "one day, maybe" 3D project that haunts me.