Seems to me you'd get to the point where you needed both pedals only to have them offset, and the only way to get on both is to release the one you're on. Like heading into a left at speed you get on the left pedal only to find that you're coming in too hot and, HOLY SMOKE I GOTTA HAVE FULL BRAKEs But with the left pedal down you can't simply roll you foot onto the right side too without losing some pedal pressure on the left. About that time there's hay flying everywhere
I could see it maybe working to some advantage via computer controls linked to the steering & speed with one pedal, but I can't see split pedals working out well. Might be fun to watch, though....