Hi urs_lesse,
I´ve already read this (Fairphone 2: New Release of Fairphone Open?) but, if I understand well, there are no answer for the question of our friend Luka.
Can he use the Android 9 Beta for his business?
I´m in the same situation too: I don´t feel safe about flashing the phone for an alternative OS which can´t work with some sensible apps like online-banking or something else.
Thanks a lot to bring us your light as you´re a reference in this forum 
Have a nice weekend