> Thanks to the mentioned LineageOS team (and many other developers at XDA forums) this otherwise "enormous undertaking" is relatively easy.
You would think so. In fact, we also thought so, when we had started our work on Android 7 for the same device a while ago.
Unfortunately, it shows that Lineage OS is by and for tech enthusiasts. There are several issues that break using this for production devices. There are a lot of stability issues that that the regular Lineage users put up with because they care more about the control they get than stability. However, the same instability is prohibitive for releasing this to regular less tech-savvy users.
The worst problem, however, is that the Lineage OS community only develops and tests with "userdebug" builds. Unfortunately, regular "user" builds don't even compile and if they do, they do not run properly. That has huge security implications (SE Linux rules, root access, etc) that we could not ignore.
That being said, having the work of the Lineage OS community available did give us a leg up. Open Source is great.