I think that’s a little backwards. Evolution is all about filling niches. The article seems to state Ediacaran diversity was driven by phenotypic (environment-induced) variation caused by ecological stressors. They claim sexual reproduction seems to be a product of environmental factors which drove the diversification.

It’s thought that the Ediacaran had fewer viable niches than the Cambrian, it’s just really not understood why that is. We don’t really see anything near that explosion in diversity again until the land-colonization of the Devonian which is kind of the same explosion driven by unoccupied niche phenomena

Few flew over the asylum nest seems too poignant