I think any further development for Fairphone 1, whether for hardware or software, should be layed in the hands of the community. Fairphone should not put more time and cost intensive resources in a smartphone that is four years old already. They just cannot afford it.
A strong commitment from the community to Lineage OS for Fairphone 2 is going on right now. So it might be possible for Fairphone 1, too, who knows? And Fairphone could better concentrate on all the other tasks which have to be done. They might be relieved to let Fairphone 1 go, knowing it will be in good hands! 