I don't think there's any sort of real limit at 30 mins. Pushing it up to an hour is still fine without having to seriously address the 'what about the bathroom!" issue. And you can go quite a way in an hour at that sort of speed. There's also the 'passenger plus' variant. If it can take 3 cars it can certainly fit a bathroom :)

But again, I'm pretty sure they if we can surmount the rest of the barriers we can solve the toilet one...