Let me try to answer to some of your questions, as best as I can
The only thing that is set in stone I think is the usage of Suru icons. Making an icon theme is long and can be tedious, let’s use the many years of excellent work from James and Sam! The rest is up to us. We can even imagine having a greyscale scalein the appmenu (look at the GNOME vanilla session) for application icons as upstream has.
The only limitation (if it’s one! ;)) is that it needs to feel “ubuntu”, meaning, The links I pasted from the ubuntu design website, the color palette, fonts and general guidelines, have to be followed IMHO to get that feeling.
This is up to you! I would really like though for openess though that we communicate on this community HUB mainly, and this is why I created this thread, some on CI, another one icon! However, you are free to create more threads in https://community.ubuntu.com/c/desktop/theme-refresh. This space is read-only for people on the hub, but write-mode for the team working on the theme. This is basically our space to communicate
In term of tools, I think what fits the best both of you (part of Canonical design team is using a pencil and scan them, another part is using Adobe, some are using the Gimp). However, it would be cool if you can export assets in a free format, like png, svg or xcf, so that the developers are able to open and see them without messing with another tool.
We can even operate as GNOME designers are doing: using a git branch and committing/sharing assets there: https://github.com/gnome-design-team/gnome-mockups/commits/master. I’m happy to create a branch in the ubuntu namespace and give you access to it if you want to.
So, we don’t move things or change any upstream behavior. We want, as @madsrh said, being close to upstream. It means that you have all CSS power in terms of transparency, border layour, gradient, colors, size and effects, but without changing the layout and placement of objects.
There has been a lot of discussion both upstream and on Fedora on this. I think we should discuss that with them (#gnome-design on gimp.net IRC network). I don’t think we should start on that front, knowing there has been multiple reluctance on this to not block us. The general idea is still to be close to upstream’s philosophy, with some ubuntu salt
I hope that answers your questions!