Users won’t buy a phone till they know that their basic set of apps are available on the device.
That pretty much rules out players like BlackBerry 10JollaUbuntu OS and Firefox OS.
Even Microsoft is still struggling.
OEMs like Samsung, HTC, LG, Sony have been hit hard by commoditization of Android. Google makes money from Google Play, cheaper phones imply more users. So, commoditization of Android OEMs is good for Google.
These OEMs have to customize Android as per Google’s requirements which have increased over time.
They cannot manufacture a competing version of Android (like Amazon’s Fire Phone) either.
This leaves us with iOS and Google-experience Android duopoly.
The only way to break that duopoly is Samsung, which is big enough that it can convince major developers to develop apps for its devices and throw money at marketing to reach out to end users.
It can make money from selling devices as well as selling apps (via app store).
A completely open source OS can pull open source developers from GNU/Linux and Android to develop it.
A completely open source OS can convince other OEMs to use it and in lieu, they can partner with Samsung on app store revenue sharing.
It remains to see what Tizen’s delayed launch eventually leads to but its a matter of survival for Samsung.