I doubt Facebook would build a hardware device. Instead, I think they'll do a 'social OS' that uses Android for all the low-level stuff, but with the Google apps all replaced with apps that have deep Facebook integration (messages, contacts, photos, etc.).

Microsoft Bing apps (e.g. Maps) could round out the features that FB doesn't build themselves, and they could use Amazon's Appstore in lieu of Android Market.

But to your point, it's possible these designers are at work making this social OS beautiful. Android in the back, iOS in the front.