@matthiss:
I think the problem is always the same as the Ubuntu Touch phone (Ubuntu phone on FP1, (similar hardware as the Aquaris E4.5 Ubuntu)).
once you’ve got the source for the SoC, you’ll need all the other source (camera, GPS, …) to get cyanogenmod working flawless on FP…
and i think that there is something going on with fairphone and cyanogen mod. The FP team never mention the ROM as something possible for our beloved phone (if you read all the statement about the future of FP, you’ll notice that Ubuntu, Firefox OS, are both considered as possibilities…this does not regard the CM).
let’s see what happend with the FP2.
also…the android one project is financed by google…that means money…a lot of (money that mediatek will enjoy a lot! 
). I think that that’s the main reason why android one will have source code released and fairphone will not