I still think it’s better to share the compiled gtk/shell theme and not your source with an installer script.
I agree, sharing the compiled css is probably easier, however you are going to gain a lot of time working on scss (I can say it’s really easy, and I didn’t do any real design work before Yaru), but it’s up to you.
The biggest part are the images which will be compiled while ninja install, right?
No, images are not compiled
So, we need to recolor the svg manually or is it possible to do it by script?
This last work on icons made me learn that always can be scripted :D, however there is nothing already in place