Thats a good idea, I've added it to our feature requests list.

You can stop users from accessing a section on the current version of CMSB by marking the section hidden under Section Editors -> Edit [section name] -> Advanced -> Hide Menu. (I've attached an example screenshot to this post)

This will stop CMS users seeing the section in their menu, but you can still access it by entering the URL for the section directly in the browser. 

Cheers,

Greg