I think we're nearing the end of Amazon not really caring about DRM. AFAIK, the DRM used by latest version of KFX files hasn't been thoroughly broken and it's a cat and mouse game now. There are some less than ideal workarounds (like downloading an older format), but you lose some of the typography improvements that Amazon only supports in KFX.

Now that Amazon seems to be interested in strong DRM, I expect a legislative solution to book DRM is our only long term hope.