I must say that, while still needs some polishing, Sailfish OS (which is not 100% free, but is quite there, and provides a complete Linux experience), does the job. My Pebble works, my BT car kit works, and I have all apps I need. In fact, my biggest complain is about the hardware, being underpowered and with an atrocious camera. An official port from Jolla to some mid level device would make me _very_ happy.
In some countries, like mine, the FOSS mobile OS killer has a name: WhatsApp. Without official support for FFOS or Ubuntu Touch, and being very aggressive against third party apps (banning their users), most people can't even think of them as an option for daily usage.
Jolla goes around this bundling a commercial Android Dalvik emulator. Not the best solution, but one quite pragmatic.