I question that math. Erasure coding needs less than half as much space as replication, and imposes pretty small costs itself. Maybe we can say the difference is irrelevant if storage prices will drop 4x over the next five years? But looking at pricing trends right now... that's not likely. Hard drives and SSDs are about the same price they were 5 years ago. The 5 years before that SSDs were seeing good advancements, but hard drive prices only advanced 2x.