Page locking alerts you if someone else is already editing a page you wish to edit.
Our Idea :
We were thinking using Jackrabbit to lock the repository of the page when someone is requesting it.
On the admininterface of the website JCR there'll be a cross (Just like when someone don't have the rights to edit the page) and the content will be accessed in "preview mode" only.
I think using a timeout for releasing the lock will be enough.