This is all very interesting news. From a sales standpoint, they're nearly admitting they cannot manage DRM properly and at Amazon scale. From a copyright standpoint, antipiracy will be extremely hard to enforce. The only middle ground is targeting honest buyers, and we all know how well that works. We should not expect this to be a permanent change. Perhaps it will be more of a very short, DRM-free golden age until another Amazon executive comes down and ends this experiment.
This is not about making all books DRM-free. It's about allowing downloads for the ones that are already DRM-free, if the publishers opt-in