The tl;dr version is that Adobe is going to start pushing for ebook vendors to provide support for the new DRM in March, and when July rolls Adobe is going to force the ebook vendors to stop supporting the older DRM. (Hadrien Gardeur, Paul Durrant, and Martyn Daniels concur on this interpretation.)

This means that any app or device which still uses the older Adobe DRM will be cut off.

via Adobe to Require New Epub DRM in July, Expects to Abandon Existing Users – The Digital Reader.