@pepijndevos I think with "Gallium" you mean Halium, which is indeed an abstraction layer between the android hardware drivers (blobs), not just LineageOS, and a normal Linux distro.
Although I don't know much about Sailfish OS, their stack seems close to ours, so you should be able to use most of their kernel code. It wouldn't be as simple as flashing a generic system image.
The rootfs is supposed to be generic, but from my experience every device needs different tweaks (so you can't just flash the rootfs), that is why the overlay method exists, which all new ports use.
You can try adapting the kernel sources to Ubuntu Touch, and then the rootfs probably from scratch. I couldn't find any port source code from Sailfish OS, as Ubuntu Touch has, which is of course necessary.
