well the problem is how close the balls are to the downward cone of the sensors. A ring would have no distance at all but could be fine.
it's the high center of gravity compared to the area of support (is there a name for that ratio? "tendency-to-roll-ratio"?) that bothers me more though. I have an SUV that I sometimes take offroad, and you really have to mind that when on a hill, SUVs are easy to roll!