Now that F-Droid Privileged Extension is built into Fairphone Open, I think F-Droid itself should be easily installable on Fairphone Open. To make that easy, we’ve made an OTA update ZIP that installs F-Droid itself:
https://f-droid.org/packages/org.fdroid.fdroid.ota/
As far as I know, this is the same kind of package that was used to install Google Play on FP1. I’m thinking there could be a similar user experience for installing F-Droid: in Fairphone Updater, the user can choose Advanced, then from there, choose the option to install F-Droid.