I installed Windows 8 Pro on my MBP Retina yesterday with only minor problems.
- Bootcamp incorrectly formatted the partition, which was easy to fix in the install process.
- Wifi was extremelly slow to connect, so much so that I resulted to seaching google to see if something major was wrong with my installation
- Scrolling was overly sensitive to the point where using the arrows was much for satisyfing
Other than that, the USB stick of course came bundled with the support which sets itself up (at least it did for me). Keyboard functions (media controls, volume, brightness, etc) and all the extra dongles (wifi [eventually], bluetooth, etc) work. I also hope to see drivers for swiping and improved scrolling in the future...would be really helpful considering the laptop cost in excess of 2.5 grand.
I don't have any answer for when support will be coming, but I'm sure you can count on this forum post for when it will be...your question was result #1 for me on Google search.