I am not so sure anymore about CyanogenMod. The FSFE says that
Newer versions [of CM] also include the proprietary Google Play services.
I think Fairphone OS is more Google free because you can choose not to let Google Services into your phone. (Also see our discussion over here)
So bottom line, I think the way to go is to make it easier to have any OS ported, not just CM. It seems far more sustainable to me.