I think just based on the general definition of "reactive" that the push idea of observer is more accurate than side-effect. I can understand that Erik may have other ideas to it and prefer a change, but I'm not so sure "side-effect" is better.
Both definitions carry a negative connotation in context; however, "side-effect" has a greater negative weight then "reactive".
If I had any opinion that mattered, as if... I would say some mathematical terms could be more relevant to describe this evolving pattern, sort of like "state functions" and "integrals"... but, for me.. reactive is fine.
well, I really enjoyed watching this...