Hi, I can help put some images together if UBports are still interested in the pi. The pi 3 is capable of armhf and arm64 so either is possible. I've quite a bit of experience at building images, an example is the unofficial xubuntu installers I made for the pi 2 + 3: https://ubuntu-mate.community/t/aarch64-on-raspberry-pi-2-rev-1-2-3b-3b/16853 . I've tried kwin under wayland on the pi3 and performance was good.
I don't know a lot about Ubuntu Touch. From my brief reading around it shouldn't be too hard to put together a 18.04 image with Unity 8. You'll have to guide me on what Ubuntu Touch brings on top of Unity, and if that can be installed outside of a phone/Android. A 16.04 image is also possible, but to get the latest vc4 graphics 18.04 would be better.
Are there any amd64 images of Ubuntu Touch/Unity 8? If not, is this something that UBports are also interested in?