It would drive around the weapon (such as 360 and Venom/Hypno-disc and Razer did), meaning pointing it would be easier than if the wheels were at the back. Only issue with the drive might be that the mass of the machine will be behind the wheels, so when you turn you'd build up lots of energy (several kilos of robot), making stopping mid-turn hard. It would tend to over-steer, I think. I guess that would make it hard to point. Hm.

Perhaps, to make use of that swinging mass, stick a massive great thwackbot-style axe on the back? Like Barnsley-bot!

It looks great, and it's certainly different. Could it not get stuck on its side?