Hi Mr. Hamano!
Here is my classic use-case: https://lore.kernel.org/git/20251219145037.17880-1-haraldnordgren@gmail.com/
I have auto-formatting set up for all the projects I work on in my daily work (Golang and TypeScript) so leading spaces do get removed automatically. But I agree with your general point, I can take a look at removing the leading column for this patch, it makes the code nicer of course! As you know, the current implementations of 'output-indicator-*' don't support empty string, so a little bit of extra work is needed for that.
Regarding "cutting from Nth column", I use macOS with iTerm 2 and I'm not sure if that functionality exists there. It's of course possible for me to keep copy-pasting the whole blob and removing the +/- signs manually or via some scripts, but seems like a lost oppornunity to not handle this from git?
Maybe I missed your point about GNU or BSD, could you explain more about that?
Harald