A foursix-person debate with the complete tickets would be pretty entertaining.
How about eight, including both the Libertarians and the Greens?
Or a four-person debate with just the presidential nominees of the four biggest parties.
I wouldn't protest. I'd like to see the Greens get into a debate at some point.
I'm actually not a proponent of "all candidates with a theoretical chance of winning should be in every debate," though. I think that would lead to an arms race of sorts, whereby ballot access alone suddenly equals a lot of publicity, leading to a lot more groups trying to get ballot access, in turn leading to
stricter ballot access laws. The current 15% polling threshold is something around 3 times too large, though, especially for the first debate in the cycle.