If you didn't read the aforelinked article, you should do so now. It looks like AMD is closer to embarking on this change that's significantly different from the status quo of having two completely different driver code-bases with one being open-source and the other not.
Posted to the XDC 2014 Bordeaux schedule is this presentation submission by AMD's Alex Deucher:
AMD's New Unified Open Source Driver
AMD is moving to unify it's current open and closed source Linux drivers over a common, shared, open source kernel driver.
This talk will provide an overview of our plans for the future and the challenges we face as we move forward.
Stay tuned to Phoronix for details next month!