A new kernel for OSX?

A research team, from the University of New South Wales, Australia, released a second version of the L4 Darwin micro-kernel codenamed Darbat last week. It's still in development stage and only manages disk and keyboard for the moment.
From a technical point of view, L4 does not replace Max OSX's XNU kernel. Indeed, it is used as a lower layer on top of which XNU runs without privileges so that if XNU crashes no KP occurs (although you indeed lose whatever was on the upper layers). Strictly speaking, it is virtualization we're talking about. L4 replaces some system calls required by XNU in order to make them more efficient. So far benchmarks tend to put both on an equal footing.
Recent events such as OSX architect Avie Tevanian's departure from Apple, numerous critical opinions (whether justified or not) on XNU's performances and XNU x86's switch to closed-source code have kindled the rumour of a kernel replacement for the versions of OSX to come. With this L4 Darwin kernel, the rumour drums are now beating although L4 does not seem to overtake XNU performance-wise.
It is, indeed, quite unlikely that Apple will change the OSX kernel in the coming months. No kernel out there is really better than the current one, for the moment. L4 development is at an early stage. As for the Linux kernel, it is covered by the GPL and Apple would have no handle and little leverage power on its development. Rewriting the kernel would be a huge task, especially if Power PC compatibility was to be kept. My guess is that the kernel will only be replaced when PPC support ends. Hopefully we'll know more about this by Apple Expo ;)
JCJ