This is a great idea and I would also suggest that it apply to the creation of anything new not only blog posts.

We definitely don't want members getting notifications to things they shouldn't have access to, due to not being able to configure access until after publishing. This is true for all content, not just blogs and forums, and this will be a priority for us to see resolved, if it's turns out to be an issue.

Does this happen in instances other than when a Blog or Forum is subscribed to?
As far as I understand, you can't subscribe to any 'containers' of content other than blogs and forums. Are there other 'containers' members can subscribe to? 

Anne, just curious why you post blog articles that aren't intended for all subscribers, if you are allowing members to subscribe to the channel. Would it work to have a separate channel for the 'post-specific' content that isn't intended for all subscribers of the channel you are posting to? Are you using post-specific access control to create sub-channels?

I posted a related request for pre-publish access control on wiki articles

Hi Trevor - In my experience users receive alerts if they are subscribed to blog, forums, documents areas/folders, galleries, wikis, and individual pages.

We don't often use blogs/forums to post articles that aren't intended for all subscribers, but occasionally someone will want to start a discussion that isn't big enough to warrant it's own channel but isn't necessarily appropriate for everyone who follows the feed it's best suited to (we use many of our blogs/forums for organizational operations stuff). In those cases it would be very useful to alert only those who have access to the post.

Hi Anne, thanks for the clarification. 

Even though members receive notifications if they are subsribed to documents, folders, galleries, wikis, and pages, I think they can only subscribe after the object has been created. Correct? There is no way for members to subscribe to a 'container' where content can get published before configuring access, causing an unwanted notification. I think this is limited to blogs and forums. I tested to see if adding a file to folder that I subscribed to generates an email notification. It looks like even though I can subscribe to a folder, when I add a file, I am not receiving a notification. If you are subscribed to a folder and add a file, do you receive a notification?

In terms of your use case to avoid these notifications being sent to unintended users, have you considered creating a hidden 'draft' channel that users are not able to subscribe to so that you can publish restricted audience content, assign access and then move it to the intended channel, to prevent notifications being sent to members they shouldn't be?