In 5 years, the Andriod OS will be fading away and Windows and iOS will be the predominant ones. Main reason: Android doesn't have a desktop interface to work/sync with well.

Hmm. I think desktop interfaces are getting less and less relevant now. If your contacts, calendars and email get synced to a web service, you could then sync them to your desktop. On Macs it's easy to set Google to provide all these, not sure how well it works with PC's.

I don't see a future for the Desktop OS as we know it now. Still there's gonne be some variant of it, since the use cases for these two are very different. For Android to survive in this world I only see the option of using some synergies with Chrome OS.

I've never actually used Chrome OS. Is there anything that makes it appealing?