I really didn't think the camera would be sensitive enough for a successful Astro camera and maybe for more distant objects the lack of lite/exposure time will be a problem but fear not some one has stopped talking about it and gone and done it with some quite lovely results.
He's doing this on his Celestron NexStar 6" with a 20 second exposure using RaspiVid.
From here he converts the video back to seperat eimages and then uses standard astronomy software to "stack" the images.
What I wonder here is weither it would be better to take a sequence of images rather than an h264 stream in terms of quality.
The only problem I see here is that there's a significant lag between executing the userspace command and the image appearing so you may be waiting quite a while
Any way Cristos's blog is here if you want the full low down