The plane refers to the plane of complex numbers (a+b*i), the right half is where the real part (a) is positive. If the zeros of your feedback loop are on the right hand side that means it is a unstable feedback loop, if they are on the left side it is stable feedback loop (this happens because the zeros eventually end up in exponents which either tend to infinity or to zero with time).
If you squint a little bit most systems looks like a feedback loop and my not very confident interpretation is, judging from the last picture, that the author thinks we have a runaway inflation problem (zeros on the right hand side of the plane) and we might or might not have the controls to move them to the left hand side to tame it.
I thought this would be something about positive zero in a 2D coordinate system, but seeing drawings of airplanes in the article I concluded “bummer, it’s not” and immediately hit backspace. Thanks for the summary. :)
If you squint a little bit most systems looks like a feedback loop and my not very confident interpretation is, judging from the last picture, that the author thinks we have a runaway inflation problem (zeros on the right hand side of the plane) and we might or might not have the controls to move them to the left hand side to tame it.