In T5029#210026, @bcooksley wrote:

How do you make guarantee that unrelated, simultaneous, uncommitted changes in the same working copy do not interfere with each other?

The problem to be solved is that workflows as I've tried to describe aren't possible. Workflows where there is no official policy that changes first have to be committed, signed off or whatever before they can be considered for inclusion upstream. Or if you want, workflows in a more relaxed community with smaller and larger contributions coming in from a wide variety of users and developers not all of whom are experts in using git, svn or what have you.

Sorry, the Root Problem was clear enough in my head but apparently not explicit enough in the OP. I hope to have addressed that now.