Installed @chrmhoffmann’s build yesterday via @z3ntu’s current TWRP over my FP Open OS 17.04.0. Had to do factory reset though (flashing the .zip would give me Error 7, after reset, it installed without any problems). I am really impressed, how well everything works already! Huge thanks to @chrmhoffmann 
Besides the small (already mentioned) inconveniences there is one issue I have not figured out yet: I have not encountered any issues yet.
I stored all media (photo, music…) on my external SD card. The card is recognized and mounted in LineageOS however without write access (Gallery can see the photos, OpenCamera cannot store them. In Lollipop I modified the platform.xml (or used the Xposed module) to grant access to the SD card.
How can I give write access to the SD card in Nougat? Since I also cannot see the /system partition in Amaze…
EDIT: I was just too dumb to make Amaze a Root Filemanager, then I could edit the /etc/permission/platform.xls and now I can store photos and listen to music.
…and something on the long run:
How will we be able to update this OS? The standard approach in the About Phone section does not seem to work…
However there is not a big hurry since the Patch level seems to be May, 5th 
Let’s hope the Fairphone devs will also jump onto the LineageOS train, now that the community served it to them on a sliver platter 