I suspect that if Amazon were to switch to ePub, which does not look likely at the moment, that we would see a rapid decline in other proprietary formats. It probably would not be as dramatic or quick as when BluRay beat out HD DVD, but it would certainly push most of the mega ebook retailers into the ePub format, as far as the American market goes. Sony and B&N are already using ePub, so if Amazon switched to ePub that would be an industry changing moment. But each would no doubt use a different DRM scheme.