Somehow the url must make clear that this is an editable link. So you need a filter on the_content that checks if there are internal links that do not yet exist. Alternatively, if you let users determine which links are editable you need to check if the url’s they give perhaps already exist. The filter should set a class on the link. Here’s a function to determine if a slug already exists:
function the_slug_exists($post_name) {
global $wpdb;
if($wpdb->get_row("SELECT post_name FROM wp_posts WHERE post_name="" . $post_name . """, 'ARRAY_A')) {
return true;
} else {
return false;
}
}
Now you get a page with links, some of which have the class editable. You can bind a javascript function to this class, which prevents normal link behaviour. You could even use it to hide the link completely for users who are not logged in. Logged in users get a little popup thats asks them if they want to create the page for the link.
The ‘yes’ button in the popup does not lead people to the url. Rather it takes the slug and adds it as a query variable to the new posts page: http://www.example.com/wp-admin/post-new.php?slug=yournewpostslug.
In your functions.php you add an action to wp_insert_post to catch the query variable and use it to fill fields in the editor. Read more about that method in @toscho ‘s anwer here. Beware that editors at this point may still change the slug, so you may want to remove that box in this case using remove_meta_box