Since we can't disable 'Register new members' access, there should be a permission to disable it. As it's for owners only.
My topic (http://www.simplemachines.org/community/index.php?topic=529120.new;topicseen#new)
Just a suggestion 8)
Cannot see this being implemented and when I was on the dev team, I would have said no - for the reasons given in topic.
You do not need to make a permission for every single thing, because that would quickly become utterly unmanageable.
In short... No.
As I already said, your concept might be true for your own forum... However, on all of the forums that I run and thousands of others, such a permission is not restricted to owners... It is granted to anyone who can manage the users....