Apart from climate change and carbon cycle issues brought up multiple times in the article, another ecologically curious function of viruses could be as a buffering function for population overgrowth which is similar in spirit if not mechanism to the predator prey relationship but can be exceedingly species specific. Efffects heavily dependent on transmission rates, population level, etc like in SIR type models. All of which could stabilize a distribution of organisms in an ecosystem (until evolution ups the ante again)

This seems like a popular thought. Parasites and disease help prevent a monoculture and encourages are healthier ecosystem. The more dominant a single species is the greater the risk that the increased density will result in disease/parasites. This accumulates over time... makes one wonder if technology is a match for whatever is coming down the pipe. Round 1 was the black plague and we didn't do so well.