Anybody have anymore info on this? I've always been under the impression that it's at least theoretically possible to copy the firmware off of something and decompile it at least.
But why start from scratch if you can just modify the existing firmware? And that seems to be perfectly possible: http://spritesmods.com/?art=hddhack
I'd say the most difficult and resource consuming part is to make versions which work on as many brands, models and revisions as possible, and make them all robust enough so they won't be detected because of random malfunctions.
But I don't know anything about hard disk firmwares: Perhaps they are not too diverse and once you know how to modify one drive, the others will follow easily?
I have personally added new functionality to binary libraries on wintel, and in embedded firmware for instance communications devices. Just jump somewhere else and jump back where you came from, there is often nothing preventing you from doing that.