To most of our users the permissions / restrictions concept is quite confusing. I like it a lot and think it makes sense, but one thing would really be very helpful:
If I want to restrict a page, I should only be able to select users who have the necessary page permissions: If I select a user for viewing in page restrictions, this user will never find the page unless he has view permission to the corresponding space.
Same thing with edit restrictions on pages: When user A has no edit permissions in the space, I can still add him for editing in page restrictions, even though this will not work,
So a message on screen or a filtered user selection in restrictions would save a lot of questions and time in our company. A lot.