@Jon: driving two wheels is actually a minor pain in the butt, mechanically speaking. You need to choose between A) drive only one of the wheels, B) force both wheels to turn at the same speed (which really sucks when one wheel is on firm ground and the other is in loose stuff), or C) add a differential ($$$ + weight).
Not that it can't be done...the old Schwinn Town & Country upright trikes had a rear differential, and there's plenty of (expensive, limited-production) trikes and quads with multiple drive wheels. It just adds complexity and cost.
I don't know about the narrow gap between the front wheels on the Juggernaut...seems like it'd be tippy. My gut instinct would be for a wide-spaced design more like the Hammerhead: