So there is no reason for an app not to work except in the specific cases you mentionned.
On point came to me when you mentionned Android 6+ : to me FairAndroid OS has been “developped” to avoid material and software obsolescence, therefore I thought it was a “universal” OS that will be updated years after years without beeing replaced by a new version (meaning you won’t have to loose or make a backup of your data before to switch to a new OS version).
As an AOSP, current FairAndroid OS is based on the 5th version of Android. It means that with apps updated to higher versions of Android, one day the current OS version will become obsolete.
So my understanding is that Fairphone is providing a LTS version (as Ubuntu) of the FairAndroid OS that will “live” as long as the Fairphone 2 will be used and repairable, and maybe depending on apps compatibility in time.
I guess it will be the case for many years.
So my question is to know if one day Fairphone will stop the current 5th Android Fairphone Open OS to replaced it by a higher version on the Fairphone 2 ?
Or will Fairphone issue a dedicated FairAndroid OS for each smartphone version ?
E.g the Fairphone 3 will come with a Android N based OS while Fairphone 2 will still be running the 5th version ?
Is Fairphone has the answer today, or is it too early ?