This is something I've been waiting for. After years of standby I've been working on Arch OS X again lately (fully operational but currently waiting for trademark approval from the Arch Linux team) and Arch Darwin is something I was contemplating to do for fun at some unspecified timeframe in the future.
If you don't mind me asking: Other than intellectual curiosity, why would you want to run Darwin, and not just one of the BSDs? Aren't a large number of the drivers still closed source?
The kext mechanism is pragmatic and interesting: as opposed to Linux kernel modules, binary kexts are compatible across whole kernel versions.
Also, having alternatives is always interesting. I was also interested in making the core of OS X† have some form of FOSS liveliness, but I've been quite disheartened about OS X and openness (however limited) since this[0] happened.
† I do believe that FOSS is very important, but I also recognise the critical effect of closed source innovations, and believe that a delicate balance and synergy between both aspects can produce fantastic results.
Strange The OSS kext I use for SMART USB HDDs [0] is also signed, but obviously not the source. You can download the compiled and signed driver here [1].
