They did. Predictably, I have been doing kernel development in MacOS since then. One drawback of doing so: when you carry a laptop, and you crash your laptop, it's rather hard to figure out *why*, as your tools for figuring it out just went away! Through the years I've tried various tools to let me emulate a Mac, seeking a way to keep a virtual Mac with me to crash and debug.
At long last, with VMware Fusion, I have that, legitimately, even. Apple has helpfully provided aid to OpenAFS development for several years now, and the availability of OSX Server from that, combined with my own $40 purchase of Fusion, finally means on my lap I have the ability to work on internals even on the occasion where I am in a car or train miles from network, or on a plane to who-knows-where.
It's been a long time coming.