shoe-horning by Sony engineers to make this work as it is. The microSD slot works, as well as Wi-Fi, GPS, Bluetooth, the notification lights and sensors. What does not run on the AOSP'd Sony Xperia Z is the camera and the modem as they use proprietary binaries that Sony does not want to release to the public. Other binaries from Sony's partners have been released but can't be part of the AOSP project because they don't use open source code. Sony is expected to replace some of these binaries with a source code the further down the road the project gets.
For now, contributions to the Sony Xperia Z will start out on Sony's own GitHub rather than the main AOSP main branch. To contribute to the cause, head over to the sourcelink and start leaving your mark on Android.
source: GitHub, SonyMobileDeveloper via TechCrunch