[Noah]

I see a few problems that you could probably work around in that design. I'm not sure how you'd do it, but I know it can be done...
1. A two wheeled robot is inherently unstable. Remember learning to ride a bike?

2. With wheels that large, why keep the bot that small? stability is the only advantage I can think of, but it seems that if the robot is smaller than the wheels your going to have a hard time stacking boxes...

3. The wheels might get in the way of things like box-grabbers if they are mounted forward backward as in your diagram.

4. Weight on the bot would have to be distributed reaally well...

5. I think the wheels would have to be one on each side, not front and back, to allow you to turn... this would also clear the front center of your robot for disadvantage # 3 in this post...