If this were implemented, I'd like the opposite - the ability to do it on one post, but not on most.
A FAQ explaining that this is not a security feature might also be good if this is done.
But I can see it being useful for a couple of non-security things. For example, for a post you want to make available initially to a limited group, then open wider at a set time; or for a "contest entries" post that you want to stop accepting comments on at a set time (if it goes - possibly temporarily, as you may bring it back later - private at that moment, that will effectively stop comments!).
no subject
A FAQ explaining that this is not a security feature might also be good if this is done.
But I can see it being useful for a couple of non-security things. For example, for a post you want to make available initially to a limited group, then open wider at a set time; or for a "contest entries" post that you want to stop accepting comments on at a set time (if it goes - possibly temporarily, as you may bring it back later - private at that moment, that will effectively stop comments!).