The primary goal for this project is to make an open source implementation of Darwin for arm. The N900 is just one of several testing platforms being used to reach this goal. As for GUI support, this should be attainable by adapting a version of OSX's IOGraphics for the kernel (apple already uses an embedded profile of IOGraphics for the iOS kernel). Also to note, some iOS kernel extensions, like AppleMobileFileIntegrity, already work without problems with this kernel.