The problem with having android as a primary OS is that it's not a lightweight 'instant' OS. You turn on your camera and you'd have to wait a significant time for android to initialize before you could take any photos.
The second problem is that android would eat up resources that would potentially be available for frame buffer storage.
The trick is to have dual OS, with the canon firmware as the primary OS with android loadable on demand. Android if loaded would reduce your image buffer size but give you greater flexibility with being able to upload to online services, use android-based image manipulation tools and, most importantly, play Angry Birds on your camera
I do see a great advantage in this and I am sure it will come.