Facebook Home = Google Toolbar
I doubt Facebook will be forking Android, or else they wouldn't call it Android. It should just be a Home Launcher with FB interface. I can already imagine it being good as I like the blue/gray designs FB is coming up lately with.
Why Forking won't work?
1. FB will have to do all the hard work that Google has done in the past 5 years to convince phone manufacturers to use FB's Android. FB will need control what the users see, but why would successful manufacturers cede control to FB, when they have more control than even Google on Android?
2. Apple Maps was the best advertisement for Google Maps and Google Services in general. Where would FB get replacements for Maps, Store? Amazon/Waze? Bing?
3. If they come up with some kind of co-branded hardware, they will have access to only a percentage of people out there who end up buying that phone. If it is moderately successful, it will manager about 10 million users in one year.
Why a simple Launcher would work?
1. Just need to enlist in Play Store. Better still it could even be part of the FB App itself.
2. Access to all the Android users around the world - 500 million users.
3. Just promote heavily within current FB app and a one click install. BOOM.
4. Control the user experience from a rival's OS. Hide all Google apps inside a drawer. FB left, right and center.
5. Already FB contacts has mobile numbers, messages, etc.
This strategy is very similar to Google's own strategy with Google Toolbar. Google collected all that data and traffic even before Chrome was born with Google toolbar.
May be in the future it can look at forking Android if Android itself becomes limiting to FB.