I get that, but darwin doesn't really work that way. Darwin doesn't truly give you an OSX user space.
Its really freakin weird and IDK why it even exists.
But here is the kicker. If you manages to get a full OSX user space to the point where you could run full dmgs to run, apple would nuke darwin.
Apple would probably break down your doors and shoot you in the middle of the night because what you will have effectively done is made OSX free and legal for anyone to install on their machine.
It would basically be a legal hackintosh.