I have a very big joint family with 9 generational records of my father's ancestors. I want to share my tree with my mother's brother so that he can add my mother's ancestors and also continue his lineage, but at the same time, I don't want him to have permission to edit my father's ancestors and lineage.
Similarly, he could share the tree with his maternal side, restricting editing access to his paternal side and so on.
I really hope you understand the need for this Restrictive Permission feature, since it would scale the shareability to the next level and thus allow generations to expand this.